fix unhandled rejection: https://travis-ci.org/wechaty/wechaty/jobs/180957671#L2789
fix unhandled rejection: https://travis-ci.org/wechaty/wechaty/jobs/180957671#L2789

mukaiu/wechaty,lijiarui/wechaty,zixia/wechaty,Chatie/wechaty,lijiarui/wechaty,wechaty/wechaty,wechaty/wechaty,mukaiu/wechaty,binsee/wechaty,Chatie/wechaty,Chatie/wechaty,wechaty/wechaty,zixia/wechaty,binsee/wechaty,mukaiu/wechaty,binsee/wechaty