[Bug Report] Cascader multi-choice mode echo tag order and incoming values are inconsistent

### Element UI version
2.13.2

### OS/Browsers version
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.70 Safari/537.36

### Vue version
2.6.10

### Reproduction Link
https://codepen.io/tianzhihen121/pen/MWwXwOK

### Steps to reproduce

Delete first tag，you will see the first tag is still exist，but the third tag is deleted.Wow!!!

I think the reason is related to cascader component defualt sortings rules，
ex:[1,2,3][1,2,4][1,2,5] order is right，but [1,2,5][1,2,4][1,2,3]，when you delete[1,2,5]，it will be wrong

Please check out,thank you!

### What is Expected?
Delete first tag,first tag will be clear, And third tag still exist.

### What is actually happening?
Delete first tag，first tag is still exist，But third tag is deleted