Store role_id as an integer instead of a string

db/schema.rb

@@ -155,7 +155,7 @@ ActiveRecord::Schema.define(:version => 20130424005701) do
   end
 
   create_table "user_role_joins", :force => true do |t|
-    t.string   "role_id"
+    t.integer  "role_id"
     t.datetime "created_at", :null => false
     t.datetime "updated_at", :null => false
     t.datetime "ends"