Prefer tap to returning

Signed-off-by: NMichael Koziarski <michael@koziarski.com>
[#3280 state:committed]

actionmailer/lib/action_mailer/helpers.rb

@@ -106,7 +106,7 @@ def inherited_with_helper(child)
     private
       # Extend the template class instance with our controller's helper module.
       def initialize_template_class_with_helper(assigns)
-        returning(template = initialize_template_class_without_helper(assigns)) do
+        initialize_template_class_without_helper(assigns).tap do |template|
           template.extend self.class.master_helper_module
         end
       end