fix: typo at guide:action_mailer_basic

Author: WongYC-66

guides/source/action_mailer_basics.md

@@ -156,7 +156,7 @@ Here is a sample HTML template that can be used for the welcome email:
   your username is: <%= @user.login %>.<br>
 </p>
 <p>
-  To login to the site, just follow this link: <%= link_to 'login`, login_url %>.
+  To login to the site, just follow this link: <%= link_to 'login', login_url %>.
 </p>
 <p>Thanks for joining and have a great day!</p>
 ```