Avoid unecessary hash allocation in AttributeMutationTracker#changes

Author: byroot

activemodel/lib/active_model/attribute_mutation_tracker.rb

@@ -26,7 +26,7 @@ def changed_values
     def changes
       attr_names.each_with_object({}.with_indifferent_access) do |attr_name, result|
         if change = change_to_attribute(attr_name)
-          result.merge!(attr_name => change)
+          result[attr_name] = change
         end
       end
     end