[Bug Report] el-table header column width and content column width are not equals

### Element UI version
2.13.2

### OS/Browsers version
Kubuntu 20.04 / Chrome 83.0.4103.61 (x64)

### Vue version
2.6.11

### Reproduction Link
https://jsfiddle.net/x4qnjfp1/2/

### Steps to reproduce
Problem with increase custom dpi on Ubuntu 20.04

### What is Expected?
Equal width column header and content

### What is actually happening?
Small, about 1px dislocation of header and content