[Bug Report] refs doClose() not expected close when popover in table

### Element UI version
0.1.0

### OS/Browsers version
Mac / Chrome

### Vue version
2.6.11

### Reproduction Link
https://jsfiddle.net/dannybook/z4wumo5k/

### Steps to reproduce
#### I use https://unpkg.com/element-ui/lib/index.js So I don't know version of `vue` and `element`

1. click `delete(删除)` then click `cancel(取消)`
2. click `status(状态)` then click `cancel(取消)`

3. Click `bug report`

4. click `delete(删除)` then click `cancel(取消)`
5. click `status(状态)` then click `cancel(取消)`

### What is Expected?
All `cancel(取消)` button can close popver.

### What is actually happening?
Some `cancel(取消)` button can not close popver.