fix non working migration

spec/factories.rb

@@ -22,15 +22,11 @@ FactoryGirl.define do
   end
 
   factory :comment do
-    commentable
+    association :commentable, factory: :debate
     user
     body 'Comment body'
   end
 
-  factory :commentable do
-    debate
-  end
-
   factory :administrator do
     user
   end