[Bug Report] messageBox延迟展示问题，每次都弹出上一次想要弹出的东西

### Mint UI version
2.2.13

### OS/Browsers version
safri11

### Vue version
2.5.2

### Reproduction Link

### Steps to reproduce
无

### What is Expected?
正常弹出messagebox.alert()、messagebox.prompt()

### What is actually happening?
延迟展示，每次都展示上一次的弹框

The report names messagebox.alert() and messagebox.prompt() but provides no reproduction link or meaningful steps. Start by locating those entry points in the messageBox component and reproducing the delayed previous-dialog behavior on the listed Vue 2.5.2 and Safari 11 setup; done means each call displays the requested dialog rather than the prior one.

Written by the indexing model from the issue text.