[2282] Bug: Live Reload works incorrectly with Vue plugin registration

Vue plugins don't deletes from Vue. Example:

const Plugin = {
  install (Vue) {
    Vue.mixin({
      created () {
        console.log('one')
      }
    })
  }
}

Vue.use(Plugin)

Add the code to plugin file and register it in nuxt.config.js

  plugins: [
    {src: '~/plugins/plugin.js'},
  ...
  ]

Start server and check logs. 'one' is appears. Then change 'one' to 'two' and wait for live reload. Reload the page. 'one' and 'two' both present in console. Expected: only 'two' appears. Nuxt version: 1.0.0-rc8