[Bug Report] Grouping table head CAN'T CLOSE

[karenlin70]

Element UI version

2.0.10

OS/Browsers version

windows/chrome 63.0.3239.84

Vue version

2.5.2

Reproduction Link

https://jsfiddle.net/suL178sv/1/

Steps to reproduce

1. just open 'https://jsfiddle.net/suL178sv/1/' and check
2. when you use el-table-column in Multi-level, it could not actually close

What is Expected?

null

What is actually happening?

when you use el-table-column in Multi-level, it could not actually close

[Leopoldthecoder]

Duplicate of #9042