++RAC to v2.2.4
++RAC to v2.2.4

nickcheng/ReactiveViewModel,iguchunhui/ReactiveViewModel,ashfurrow/ReactiveViewModel,SummerHanada/ReactiveViewModel,fxd/ReactiveViewModel,takeshineshiro/ReactiveViewModel,nickcheng/ReactiveViewModel,jackgao2016/ReactiveViewModel,ReactiveCocoa/ReactiveViewModel,SummerHanada/ReactiveViewModel,takeshineshiro/ReactiveViewModel,ashfurrow/ReactiveViewModel,iguchunhui/ReactiveViewModel,ReactiveCocoa/ReactiveViewModel,nickcheng/ReactiveViewModel,fxd/ReactiveViewModel,jackgao2016/ReactiveViewModel