Include table name in query for only_deleted

Fixes #27

lib/paranoia.rb

@@ -7,8 +7,9 @@ module Paranoia
     def paranoid? ; true ; end
 
     def only_deleted
-      scoped.tap { |x| x.default_scoped = false }.where("deleted_at is not null")
+      scoped.tap { |x| x.default_scoped = false }.where("#{self.table_name}.deleted_at is not null")
     end
+
     def with_deleted
       scoped.tap { |x| x.default_scoped = false }
     end