[Bug Report] Cann't adjust width of column, when add css "zoom:0.9" to parent of table

### Element UI version
0.1.0

### OS/Browsers version
Chrome

### Vue version
2.6.11

### Reproduction Link
https://codepen.io/guankaomeng/pen/VwYQXvG

### Steps to reproduce
1、create a table with attr "border"
2、add a parent div for the table with css "zoom: 0.9"
3、now cann't adjust width of the table column

### What is Expected?
can adjust width of table when css "zoom: 0.9" is set

### What is actually happening?
width of the table column cann't be adjusted