[Bug Report] el-Table not smooth

### Element UI version
2.13.2

### OS/Browsers version
electron 9.3.0

### Vue version
2.6.12

### Reproduction Link
https://jsfiddle.net/of3609ut/

### Steps to reproduce
Fast scrolling left and right

### What is Expected?
Synchronous scrolling of header, body and total

### What is actually happening?
The body rolls faster than the head and total（当把整个table作为横向滚动对象时，因为fixed的列在table内，导致无法真正fixed，但是解决滚动不同步问题）