Add missing attribute in README example

Author: oboxodo

README.md

@@ -58,7 +58,7 @@ $ bundle install
 
 ```ruby
 class Movie
-  attr_accessor :id, :name, :year, :actor_ids, :owner_id
+  attr_accessor :id, :name, :year, :actor_ids, :owner_id, :movie_type_id
 end
 ```