[Bug Report] Popup组件动画在ios版微信中不流畅

### Mint UI version
2.2.13

### OS/Browsers version
IOS 11.2.2/微信 WeChat 6.6.1

### Vue version
2.5.13

### Reproduction Link
[http://elemefe.github.io/mint-ui/#/popup](http://elemefe.github.io/mint-ui/#/popup)

### Steps to reproduce
在IOS微信中打开，点击 下侧弹出popup，动画不流畅，可对比safari浏览器

### What is Expected?
动画流畅

### What is actually happening?
动画不流畅