[Bug Report] 将popup作为组件封装会无法关闭

### Mint UI version
2.2.13

### OS/Browsers version
win7 64位 谷歌 66.0.3359.181

### Vue version
2.5.16

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

### Steps to reproduce

confirm () {
this.visible = false
// this.$emit('confirm', this.currentValue)
}
外部引用时无法关闭

### What is Expected?
popup可以正常关闭

### What is actually happening?
popup无法关闭，visible的值无法改变