refactor(SidebarItem): optimizate SidebarItem (#845)

* 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 cef02a30b0.

* fix: complement i18n text.

src/lang/zh.js

@@ -29,9 +29,13 @@ export default {
     mixChart: '混合图表',
     example: '综合实例',
     nested: '路由嵌套',
-    bar: 'Bar',
-    barProfile: 'Profile',
-    barPosts: 'Posts',
+    menu1: '菜单1',
+    'menu1-1': '菜单1-1',
+    'menu1-2': '菜单1-2',
+    'menu1-2-1': '菜单1-2-1',
+    'menu1-2-2': '菜单1-2-2',
+    'menu1-3': '菜单1-3',
+    menu2: '菜单2',
     Table: 'Table',
     dynamicTable: '动态Table',
     dragTable: '拖拽Table',