706_缓存路由组件

作用：

让不展示的路由组件保持挂载，不被销毁

缓存一个组件

<keep-alive include="News">
    <router-view></router-view>
</keep-alive>

缓存多个组件

<keep-alive :include="['News','Message']">
    <router-view></router-view>
</keep-alive>