When [bug report] uses El steps, if part of the El steps are loaded asynchronously, there will be a bug of step state matching error

### Element UI version
2.13.1

### OS/Browsers version
win10 64位/chrome v81.0.4044.113

### Vue version
2.6.11

### Reproduction Link
https://codepen.io/pen/?&editable=true=https%3A%2F%2Felement.eleme.cn%2F

### Steps to reproduce
el-step 首尾步骤是写死的，中间步骤是异步加载的，此时 el-steps 的进度和状态匹配会出现错乱

### What is Expected?
异步加载后的 el-step 也能正常匹配

### What is actually happening?
使用 vue-developtool 查看发现，el-steps 的 el-step 树排序是写死的树（两个节点）后加上异步加载的树，顺序是错的，所以匹配出现问题