minor spacing fix in code example in ActionMailer::Base.

actionmailer/lib/action_mailer/base.rb

@@ -22,16 +22,16 @@ module ActionMailer #:nodoc:
   #
   # Examples:
   #
-  #  class Notifier < ActionMailer::Base
-  #    default :from => 'no-reply@example.com',
+  #   class Notifier < ActionMailer::Base
+  #     default :from => 'no-reply@example.com',
   #            :return_path => 'system@example.com'
   #
-  #    def welcome(recipient)
-  #      @account = recipient
-  #      mail(:to => recipient.email_address_with_name,
-  #           :bcc => ["bcc@example.com", "Order Watcher <watcher@example.com>"])
-  #      end
-  #    end
+  #     def welcome(recipient)
+  #       @account = recipient
+  #       mail(:to => recipient.email_address_with_name,
+  #            :bcc => ["bcc@example.com", "Order Watcher <watcher@example.com>"])
+  #     end
+  #   end
   #
   # Within the mailer method, you have access to the following methods:
   #