[bug report] carousel renders El carousel item according to array. After partial data of array changes, El carousel item does not switch left and right according to array order

### Element UI version
2.13.2

### OS/Browsers version
window 10 / chrome 70

### Vue version
3.0.0-beta.20

### Reproduction Link
https://codepen.io/jian-yin/pen/ExPLpjW?editable=true%3Dhttps%3A%2F%2Felement.eleme.cn%2F

### Steps to reproduce
1、data 定义数组 list = [1,3,5,7]
2、mounted 后 this.list = [1,2,3,4]

### What is Expected?
Carousel 切换顺序 1,2,3,4

### What is actually happening?
Carousel 切换顺序 1,3,2,4