Fixed quotes in environment example in Rails Application Templates guide.

guides/source/rails_application_templates.md

@@ -91,7 +91,7 @@ Adds a line inside the `Application` class for `config/application.rb`.
 If `options[:env]` is specified, the line is appended to the corresponding file in `config/environments`.
 
 ```ruby
-environment 'config.action_mailer.default_url_options = {host: 'http://yourwebsite.example.com'}, env: 'production'
+environment 'config.action_mailer.default_url_options = {host: "http://yourwebsite.example.com"}', env: 'production'
 ```
 
 A block can be used in place of the `data` argument.