fix bug in CoreDataStack
fix bug in CoreDataStack

artemkalinovsky/JSQCoreDataKit,jessesquires/JSQCoreDataKit,saurabytes/JSQCoreDataKit,jessesquires/JSQCoreDataKit,jessesquires/JSQCoreDataKit,artemkalinovsky/JSQCoreDataKit,artemkalinovsky/JSQCoreDataKit,saurabytes/JSQCoreDataKit,pajai/JSQCoreDataKit,pajai/JSQCoreDataKit