[Bug Report] select options dropdown displayed every time clicked browser`s page tab and click back

### Element UI version
2.13.0

### OS/Browsers version
Windows 10 / Edge 80.0.361.69 based on Chromium

### Vue version
2.6.11

### Reproduction Link
https://codepen.io/bear2leaf/pen/JjdzPdp

### Steps to reproduce
1.use el-select and enable filterable
2.select one option
3.click browser`s other tab
4.click previous tab (which contains our el-select component)
5.the select options dropdown will auto display

### What is Expected?
the select options dropdown will not auto display when click back browser`s tab

### What is actually happening?
the select options dropdown will auto display when click back browser`s tab