Merge pull request rails#5729 from oscardelben/use_tap

Use the more idiomatic tap method

Author: josevalim

activemodel/lib/active_model/attribute_methods.rb

@@ -255,11 +255,7 @@ def undefine_attribute_methods
 
       # Returns true if the attribute methods defined have been generated.
       def generated_attribute_methods #:nodoc:
-        @generated_attribute_methods ||= begin
-          mod = Module.new
-          include mod
-          mod
-        end
+        @generated_attribute_methods ||= Module.new.tap { |mod| include mod }
       end
 
       protected