Update generators to use new defaults.

railties/lib/generators/rails/mailer/templates/mailer.rb

@@ -1,5 +1,5 @@
 class <%= class_name %> < ActionMailer::Base
-  self.defaults = { :from => "from@example.com" }
+  self.defaults :from => "from@example.com"
 <% for  action in actions -%>
 
   # Subject can be set in your I18n file at config/locales/en.yml

railties/test/generators/mailer_generator_test.rb

@@ -9,7 +9,7 @@ class MailerGeneratorTest < Rails::Generators::TestCase
     run_generator
     assert_file "app/mailers/notifier.rb" do |mailer|
       assert_match /class Notifier < ActionMailer::Base/, mailer
-      assert_match /self\.defaults\ =\ \{\ :from\ =>\ "from@example\.com"\ \}/, mailer
+      assert_match /self\.defaults :from => "from@example.com"/, mailer
     end
   end