[Bug Report] Width Rendering of el-table Components under IE11

### Element UI version
2.13.0

### OS/Browsers version
win10 / IE11

### Vue version
2.4.4

### Reproduction Link
https://jsfiddle.net/wwt1995/e3n24suf/

### Steps to reproduce
step1: 在ie11上打开element官方文档进入table的demo
step2: 查看前几个列少的table 宽度无法自适应

### What is Expected?
IE11 宽度能够自适应填充满容器

### What is actually happening?
IE11 宽度未能自适应