fix #40 (typescript bug)
fix #40 (typescript bug)

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