* refactor(sidebar-item): optimizate SiderbarItem.

* chore: update nested examples.

* fix: fix a wrong path.

* fix: fix a transition bug.

* fix: fix a wrong path.

* perf: using "router" mode of el-menu.

* Revert "perf: using "router" mode of el-menu."

This reverts commit cef02a30b02a31242521e9e678cfeaad6f09448c.

* fix: complement i18n text.

* fix filename bug

* format

* format

* refine style

* refine 404 style

* refine

Detail see [Runtime-Compiler-vs-Runtime-only](https://vuejs.org/v2/guide/installation.html#Runtime-Compiler-vs-Runtime-only)

When get rich editor value(null) from backend,it will occur error
```
Error in nextTick: "TypeError: Cannot read property 'replace' of null"
```
So I set val to '' to avoid it