fix[Sidebar]: fixed nested router hover bug

Author: PanJiaChen

src/views/layout/components/Sidebar/SidebarItem.vue

@@ -9,7 +9,7 @@
       </app-link>
     </template>
 
-    <el-submenu v-else ref="subMenu" :index="resolvePath(item.path)">
+    <el-submenu v-else ref="subMenu" :index="resolvePath(item.path)" popper-append-to-body>
       <template slot="title">
         <item v-if="item.meta" :icon="item.meta && item.meta.icon" :title="generateTitle(item.meta.title)" />
       </template>