[Bug Report] Indicator组件在iPhone4s上有时无法关闭

### Mint UI version
2.2.7

### OS/Browsers version
ios 8.1.3

### Vue version
2.3.3

### Reproduction Link
[https://github.com/ElemeFE/mint-ui](https://github.com/ElemeFE/mint-ui)

### Steps to reproduce
app里面镶嵌h5页面，h5页面引用了mint-ui的Indicator组件，Indicator.close()在iPhone4s上有时无法关闭，Indicator一直在开启状态

### What is Expected?
在iPhone4s上Indicator.close()能够关闭

### What is actually happening?
Indicator一直在开启状态，Indicator.close()无法关闭