修复TopNav无法正确获取active的问题

Signed-off-by: Lyb刘同学 <1553592282@qq.com>

@@ -14,7 +14,7 @@
     </template>
 
     <!-- 顶部菜单超出数量折叠 -->
-    <el-submenu :style="{'--theme': theme}" index="more" v-if="topMenus.length > visibleNumber">
+    <el-submenu :style="{'--theme': theme}" index="more" :key="visibleNumber" v-if="topMenus.length > visibleNumber">
       <template slot="title">更多菜单</template>
       <template v-for="(item, index) in topMenus">
         <el-menu-item