Add bootstrap 4 on NuxtJS

nuxt.config.js

...
  head: {
    title: 'example',
    meta: [
      { charset: 'utf-8' },
      { name: 'viewport', content: 'width=device-width, initial-scale=1' },
      { hid: 'description', name: 'description', content: 'Nuxt.js project' },

      // example vue-meta
      { hid: 'title', name: 'title', content: 'Nuxt.js project' }
    ],
    link: [
      { rel: 'icon', type: 'image/x-icon', href: '/favicon.ico' },
      { rel: 'stylesheet', type: 'text/css', href: 'https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.0.0-beta.3/css/bootstrap.min.css' }
    ]
  },
...