Update AM example

Author: avakhov

actionmailer/README.rdoc

@@ -22,12 +22,12 @@ the email.
 This can be as simple as:
 
   class Notifier < ActionMailer::Base
-    delivers_from '[email protected]'
+    default from: '[email protected]'
 
     def welcome(recipient)
       @recipient = recipient
-      mail(:to => recipient,
-           :subject => "[Signed up] Welcome #{recipient}")
+      mail(to: recipient,
+           subject: "[Signed up] Welcome #{recipient}")
     end
   end