[1132] extendRoutes doesn't work?

nuxt.config.js： router: { extendRoutes(routes) { routes: [{ path: '/', redirect: '/lines' }] } }

index.vue：

<template>
  <div>
    <ul class="m-tag">
      <nuxt-link :to="item.link" v-for="item in navList" :key="item.title" active-class="act">
        {{ item.title }}
      </nuxt-link>
    </ul>
    <nuxt-child/>
  </div>
</template>

<script>

export default {
  head () {
    return {
      meta: [
        { hid: 'description', name: 'description', content: 'My custom description' }
      ]
    }
  },
  data () {
    return {
      navList: [{
        title: 'lines',
        link: '/lines'
      }, {
        title: 'traffic',
        link: '/traffic'
      }]
    }
  }
}
</script>

when I visit "http://127.0.0.1:3000"，I expect "http://127.0.0.1:3000/lines"

but it doesn't work.