load hooks return ActiveRecord::Model in Rails 4, use Concern

lib/cancan/model_adapters/active_record_adapter.rb

@@ -165,6 +165,8 @@ module CanCan
   end
 end
 
+ActiveSupport.on_load(:active_record) do
   ActiveRecord::Base.class_eval do
     include CanCan::ModelAdditions
   end
+end

lib/cancan/model_additions.rb

@@ -2,6 +2,8 @@ module CanCan
 
   # This module adds the accessible_by class method to a model. It is included in the model adapters.
   module ModelAdditions
+    extend ActiveSupport::Concern
+
     module ClassMethods
       # Returns a scope which fetches only the records that the passed ability
       # can perform a given action on. The action defaults to :index. This
@@ -23,9 +25,5 @@ module CanCan
         ability.model_adapter(self, action).database_records
       end
     end
-
-    def self.included(base)
-      base.extend ClassMethods
-    end
   end
 end