[ci skip] Include ActiveModel::Model in a class instead of inheriting

activemodel/lib/active_model/naming.rb

@@ -218,10 +218,11 @@ module ActiveModel
     # used to retrieve all kinds of naming-related information
     # (See ActiveModel::Name for more information).
     #
-    #   class Person < ActiveModel::Model
+    #   class Person
+    #     include ActiveModel::Model
     #   end
     #
-    #   Person.model_name          # => Person
+    #   Person.model_name.name     # => "Person"
     #   Person.model_name.class    # => ActiveModel::Name
     #   Person.model_name.singular # => "person"
     #   Person.model_name.plural   # => "people"