nav do not display in the internationalized mode

[finch001]

• Mac OS
• node v8.9.0
• VuePress 0.7.0
• chrome Version 65.0.3325.181
• global install
• yarn

// .vuepress/config.js
module.exports = {
  locales: {
    '/': {
      lang: 'en-US',
      title: 'VuePress',
      description: 'Vue-powered Static Site Generator'
    },
    '/zh/': {
      lang: 'zh-CN',
      title: 'VuePress',
      description: 'Vue 驱动的静态网站生成器'
    }
  },
  themeConfig: {
    locales: {
      '/': {
        selectText: 'Languages',
        label: 'English',
        nav: [
          {
            text: 'Home',
            link: '/'
          }, {
            text: 'Guide',
            link: '/guide/'
          }, {
            text: 'External',
            link: 'https://google.com'
          }
        ]
      },
      '/zh/': {
        selectText: '选择语言',
        label: '简体中文',
        nav: [
          {
            text: 'Home',
            link: '/zh/'
          }
        ]
      }
    }
  }
}

Project layout
.
├── README.md
├── guide
│   ├── README.md
│   ├── one.md
│   └── two.md
├── practise
│   └── README.md
└── zh
    ├── README.md
    └── hello.md