I added that line but I’m getting an error.

This is what my config looks like:

(use-package yasnippet 
:bind ("C-c e" . yas-load-snippet-buffer)
:init
(yas-global-mode 1) 

:config 
;; load yasnippet directories
(setq yas-snippet-dirs '("~/emacs/interesting-snippets" "~/emacs/snippets"))

;; don't insert random spaces in my prose
(setq yas-indent-line (quote none)) 

;; take input word including hyphen.
(setq yas/key-syntaxes '("w_" "w_." "^ ")) ; default is '("w" "w_" "w_." "^ ")

;; suppress backquote warnings
(add-to-list 'warning-suppress-types '(yasnippet backquote-change)) 
)

And this is the error I get:

Debugger entered--Lisp error: (void-variable warning-suppress-types)
 (member (quote (yasnippet backquote-change)) warning-suppress-types)
 (if (member (quote (yasnippet backquote-change)) warning-suppress-types) warning-suppress-types (setq warning-suppress-types (cons (quote (yasnippet backquote-change)) warning-suppress-types)))
 (progn (setq yas-snippet-dirs (quote ("~/emacs/interesting-snippets" "~/emacs/snippets"))) (setq yas-indent-line (quote none)) (setq yas/key-syntaxes (quote ("w_" "w_." "^ "))) (if (member (quote (yasnippet backquote-change)) warning-suppress-types) warning-suppress-types (setq warning-suppress-types (cons (quote (yasnippet backquote-change)) warning-suppress-types))))
 (condition-case err (progn (setq yas-snippet-dirs (quote ("~/emacs/interesting-snippets" "~/emacs/snippets"))) (setq yas-indent-line (quote none)) (setq yas/key-syntaxes (quote ("w_" "w_." "^ "))) (if (member (quote (yasnippet backquote-change)) warning-suppress-types) warning-suppress-types (setq warning-suppress-types (cons (quote (yasnippet backquote-change)) warning-suppress-types)))) ((debug error) (ignore (display-warning (quote use-package) (format "%s %s: %s" "yasnippet" ":config" (error-message-string err)) :error))))
 (progn (condition-case err (progn (setq yas-snippet-dirs (quote ("~/emacs/interesting-snippets" "~/emacs/snippets"))) (setq yas-indent-line (quote none)) (setq yas/key-syntaxes (quote ("w_" "w_." "^ "))) (if (member (quote (yasnippet backquote-change)) warning-suppress-types) warning-suppress-types (setq warning-suppress-types (cons (quote (yasnippet backquote-change)) warning-suppress-types)))) ((debug error) (ignore (display-warning (quote use-package) (format "%s %s: %s" "yasnippet" ":config" (error-message-string err)) :error)))) t)
 (lambda nil (progn (condition-case err (progn (setq yas-snippet-dirs (quote ("~/emacs/interesting-snippets" "~/emacs/snippets"))) (setq yas-indent-line (quote none)) (setq yas/key-syntaxes (quote ("w_" "w_." "^ "))) (if (member (quote (yasnippet backquote-change)) warning-suppress-types) warning-suppress-types (setq warning-suppress-types (cons (quote ...) warning-suppress-types)))) ((debug error) (ignore (display-warning (quote use-package) (format "%s %s: %s" "yasnippet" ":config" (error-message-string err)) :error)))) t))()
 eval-after-load(yasnippet (lambda nil (progn (condition-case err (progn (setq yas-snippet-dirs (quote ("~/emacs/interesting-snippets" "~/emacs/snippets"))) (setq yas-indent-line (quote none)) (setq yas/key-syntaxes (quote ("w_" "w_." "^ "))) (if (member (quote (yasnippet backquote-change)) warning-suppress-types) warning-suppress-types (setq warning-suppress-types (cons (quote ...) warning-suppress-types)))) ((debug error) (ignore (display-warning (quote use-package) (format "%s %s: %s" "yasnippet" ":config" (error-message-string err)) :error)))) t)))
 (progn (if (fboundp (quote yas-load-snippet-buffer)) nil (autoload (function yas-load-snippet-buffer) "yasnippet" nil t)) (condition-case err (yas-global-mode 1) ((debug error) (ignore (display-warning (quote use-package) (format "%s %s: %s" "yasnippet" ":init" (error-message-string err)) :error)))) (eval-after-load (quote yasnippet) (function (lambda nil (progn (condition-case err (progn (setq yas-snippet-dirs ...) (setq yas-indent-line ...) (setq yas/key-syntaxes ...) (if ... warning-suppress-types ...)) ((debug error) (ignore ...))) t)))) (ignore (let* ((name "C-c e") (key (if (vectorp name) name (read-kbd-macro name))) (kdesc (cons (if (stringp name) name (key-description name)) (quote nil))) (binding (lookup-key (or nil global-map) key))) (add-to-list (quote personal-keybindings) (list kdesc (quote yas-load-snippet-buffer) (if (numberp binding) nil binding))) (define-key (or nil global-map) key (quote yas-load-snippet-buffer)))))
 eval-buffer(#<buffer *load*-133122> nil "/Users/jay/emacs/prelude/personal/shared-functions.el" nil t) ; Reading at buffer position 107178
 load-with-code-conversion("/Users/jay/emacs/prelude/personal/shared-functions.el" "/Users/jay/emacs/prelude/personal/shared-functions.el" nil nil)
 load("/Users/jay/emacs/prelude/personal/shared-functions.el" nil nil t)
 load-file("/Users/jay/emacs/prelude/personal/shared-functions.el")
 org-babel-load-file("~/emacs/prelude/personal/shared-functions.org")
 eval-buffer(#<buffer *load*-611316> nil "/Users/jay/emacs/maximal/maximal-init.el" nil t) ; Reading at buffer position 592
 load-with-code-conversion("/Users/jay/emacs/maximal/maximal-init.el" "/Users/jay/emacs/maximal/maximal-init.el" nil nil)
 load("/Users/jay/emacs/maximal/maximal-init.el")
 eval-buffer(#<buffer *load*> nil "/Users/jay/.emacs.d/init.el" nil t) ; Reading at buffer position 4994
 load-with-code-conversion("/Users/jay/.emacs.d/init.el" "/Users/jay/.emacs.d/init.el" t t)
 load("/Users/jay/.emacs.d/init" t t)
 #[0 "\205\262	\306=\203\307\310Q\202;	\311=\204\307\312Q\202;\313\307\314\315#\203*\316\202;\313\307\314\317#\203:\320\nB\321\202;\316\322\323
\322\211#\210\322=\203a\324\325\326\307\327Q!\"\323
\322\211#\210\322=\203`
\210\203\243\330!\331\232\203\243\332!\211\333P\334
!\203}\211\202\210\334!\203\207
\202\210\314\262
\203\241\335\"\203\237\336\337#\210\340\341!\210
\266\f?\205\260\314\323\342\322\211#)\262
\207" [init-file-user system-type delayed-warnings-list user-init-file inhibit-default-init inhibit-startup-screen ms-dos "~" "/_emacs" windows-nt "/.emacs" directory-files nil "^\\.emacs\\(\\.elc?\\)?$" "~/.emacs" "^_emacs\\(\\.elc?\\)?$" (initialization "`_emacs' init file is deprecated, please use `.emacs'") "~/_emacs" t load expand-file-name "init" file-name-as-directory "/.emacs.d" file-name-extension "elc" file-name-sans-extension ".el" file-exists-p file-newer-than-file-p message "Warning: %s is newer than %s" sit-for 1 "default"] 7 "\n\n(fn)"]()
 #[0 "\300 \210\302\211\207" [#[0 "\205\262	\306=\203\307\310Q\202;	\311=\204\307\312Q\202;\313\307\314\315#\203*\316\202;\313\307\314\317#\203:\320\nB\321\202;\316\322\323
\322\211#\210\322=\203a\324\325\326\307\327Q!\"\323
\322\211#\210\322=\203`
\210\203\243\330!\331\232\203\243\332!\211\333P\334
!\203}\211\202\210\334!\203\207
\202\210\314\262
\203\241\335\"\203\237\336\337#\210\340\341!\210
\266\f?\205\260\314\323\342\322\211#)\262
\207" [init-file-user system-type delayed-warnings-list user-init-file inhibit-default-init inhibit-startup-screen ms-dos "~" "/_emacs" windows-nt "/.emacs" directory-files nil "^\\.emacs\\(\\.elc?\\)?$" "~/.emacs" "^_emacs\\(\\.elc?\\)?$" (initialization "`_emacs' init file is deprecated, please use `.emacs'") "~/_emacs" t load expand-file-name "init" file-name-as-directory "/.emacs.d" file-name-extension "elc" file-name-sans-extension ".el" file-exists-p file-newer-than-file-p message "Warning: %s is newer than %s" sit-for 1 "default"] 7 "\n\n(fn)"] init-file-had-error nil] 2 "\n\n(fn)"]()
 funcall(#[0 "\300 \210\302\211\207" [#[0 "\205\262	\306=\203\307\310Q\202;	\311=\204\307\312Q\202;\313\307\314\315#\203*\316\202;\313\307\314\317#\203:\320\nB\321\202;\316\322\323
\322\211#\210\322=\203a\324\325\326\307\327Q!\"\323
\322\211#\210\322=\203`
\210\203\243\330!\331\232\203\243\332!\211\333P\334
!\203}\211\202\210\334!\203\207
\202\210\314\262
\203\241\335\"\203\237\336\337#\210\340\341!\210
\266\f?\205\260\314\323\342\322\211#)\262
\207" [init-file-user system-type delayed-warnings-list user-init-file inhibit-default-init inhibit-startup-screen ms-dos "~" "/_emacs" windows-nt "/.emacs" directory-files nil "^\\.emacs\\(\\.elc?\\)?$" "~/.emacs" "^_emacs\\(\\.elc?\\)?$" (initialization "`_emacs' init file is deprecated, please use `.emacs'") "~/_emacs" t load expand-file-name "init" file-name-as-directory "/.emacs.d" file-name-extension "elc" file-name-sans-extension ".el" file-exists-p file-newer-than-file-p message "Warning: %s is newer than %s" sit-for 1 "default"] 7 "\n\n(fn)"] init-file-had-error nil] 2 "\n\n(fn)"])
 command-line()
 normal-top-level()