[Bug Report] tabs's el-tab-pane contains V-IF instructions which can cause location disorder.

[vasttian]

Element UI version

2.4.5

OS/Browsers version

Hight Sierra 10.13.6 / Chrome 67.0.3396.99

Vue version

2.5.17

Reproduction Link

https://jsfiddle.net/vasttian/8kpc2m1n/9/

Steps to reproduce

run

找到了之前关于此问题的修复，#6066
在 element/packages/tabs/src/tabs.vue 的 addPanes 方法里
使用之前修复的代码测试顺序正常，
但是最新的版本直接使用 indexOf 去寻找 index，导致找出的 index 错误。
最终导致顺序错乱。

What is Expected?

tab pane 顺序正常。

What is actually happening?

tab pane 顺序错乱。

[element-bot]

Translation of this issue:

Element UI version
2.4.5

OS/Browsers version
Hight Sierra 10.13.6 / Chrome 67.0.3396.99

Vue version
2.5.17

Reproduction Link
https://jsfiddle.net/vasttian/8kpc2m1n/9/

Steps to reproduce
Run

The previous repair of this problem was found, #6066.
In the element/packages/tabs/src/tabs.vue [addPanes](https://github.com/ElemeFE/element/blob/dev/packages/tabs/src/tabs.vue L91-L94) method

The code that was repaired with before was tested in good order.
But the latest version uses indexOf directly to search for index, leading to index errors identified.

In the end, the sequence was disorderly.
What is Expected?

The order of tab pane is normal.
What is actually happening?

The sequence of tab pane is disorderly.

[goatandsheep]

It's a v-show actually, which is annoying because it renders all the tabs, but doesn't make them visible