Default deployment problem of [bug report] navigation menu

### Element UI version
2.13.2

### OS/Browsers version
Chrome/74.0.3729.131

### Vue version
3.0.0-beta.14

### Reproduction Link
https://codepen.io/ck0904/pen/pogorpZ

### Steps to reproduce
打开页面默认展开item，点击收起，导航页面收起。再点击展开，导航菜单展开但default-openeds设置的展开项并没有生效。

### What is Expected?
导航菜单再次展开时default-openeds设置的展开项生效

### What is actually happening?
导航菜单展开但default-openeds设置的展开项并没有生效