[bug report] El submenu drop-down menu sub item the mobile terminal needs to click twice to hide the drop-down menu layer

### Element UI version
2.13.2

### OS/Browsers version
ios/andriod wechat or qq browser safri

### Vue version
2.5.20

### Reproduction Link
https://codepen.io/dickynet/pen/qBbqQRJ?editable=true%3Dhttps%3A%2F%2Felement.eleme.cn%2F

### Steps to reproduce
点击我的工作台中的任何一个下拉菜单项目

### What is Expected?
点击菜单项后隐藏下拉层

### What is actually happening?
第一次点击菜单项不隐藏，需要第二次点击才隐藏。