Error when trying to use scoped styles with vuejs and node-sass

app.js

var Vue = require('vue');
var App =  require('../../components/app.vue');

new Vue(App).$mount('#app')

app.vue

<style lang="sass" scoped>
  @import './resources/assets/sass/variables/colours';
  @import './resources/assets/sass/helpers/colour';

  .viewport {
    display: flex;

    flex: 1;

    width: 100vw;
    height: 100vh;

    .view {
      display: flex;
      flex: 1;
      height: 10vh;
      background: colour('x');
    }

    > div {
      flex: 1;
    }

  }
</style>

<template>
  <div class="viewport">
    <div class="view">
      <appbar></appbar>
      <div class="sidebar"></div>
      <div class="filter"></div>
      <div class="content"></div>
    </div>
  </div>
</template>

<script>
  var appbar = require('./appbar.vue');

  export default {
    name: 'App',
    components: {
      appbar
    }
  }
</script>

appbar.vue

<style lang="sass" scoped>
  .appbar {
    background: #99cc00;
    height: 5vh;
  }
</style>

<template>
  <div>
    <div class="appbar really">
      This is the new appbar
    </div>
  </div>
</template>

<script>
  export default {
    name: 'appbar'
  }
</script>

error.log

TypeError: Cannot read property 'valueOf' of undefined
    at tokenize (/home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/node_modules/postcss-selector-parser/dist/tokenize.js:34:24)
    at new Parser (/home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/node_modules/postcss-selector-parser/dist/parser.js:89:49)
    at Processor.process (/home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/node_modules/postcss-selector-parser/dist/processor.js:36:25)
    at /home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/lib/style-rewriter.js:15:10
    at Root.each (/home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/node_modules/postcss/lib/container.js:58:22)
    at /home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/lib/style-rewriter.js:8:10
    at LazyResult.run (/home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/node_modules/postcss/lib/lazy-result.js:201:20)
    at /home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/node_modules/postcss/lib/lazy-result.js:115:37
    at LazyResult.asyncTick (/home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/node_modules/postcss/lib/lazy-result.js:129:15)
    at processing.Promise.then._this2.processed (/home/vagrant/Code/backoffice/node_modules/laravel-elixir/node_modules/vueify/node_modules/postcss/lib/lazy-result.js:155:20)
[08:51:09] gulp-notify: [Laravel Elixir] Browserify Failed!: Cannot read property 'valueOf' of undefined while parsing file: /home/vagrant/Code/backoffice/resources/components/appbar.vue
{ [TypeError: Cannot read property 'valueOf' of undefined while parsing file: /home/vagrant/Code/backoffice/resources/components/appbar.vue]
  filename: '/home/vagrant/Code/backoffice/resources/components/appbar.vue',
  stream:
   Labeled {
     _readableState:
      ReadableState {
        highWaterMark: 16,
        buffer: [],
        length: 0,
        pipes: [Object],
        pipesCount: 1,
        flowing: true,
        ended: false,
        endEmitted: false,
        reading: true,
        sync: false,
        needReadable: true,
        emittedReadable: false,
        readableListening: false,
        objectMode: true,
        defaultEncoding: 'utf8',
        ranOut: false,
        awaitDrain: 0,
        readingMore: false,
        decoder: null,
        encoding: null,
        resumeScheduled: false },
     readable: true,
     domain: null,
     _events:
      { end: [Object],
        error: [Object],
        data: [Function: ondata],
        _mutate: [Object] },
     _eventsCount: 4,
     _maxListeners: undefined,
     _writableState:
      WritableState {
        highWaterMark: 16,
        objectMode: true,
        needDrain: false,
        ending: true,
        ended: true,
        finished: true,
        decodeStrings: true,
        defaultEncoding: 'utf8',
        length: 0,
        writing: false,
        corked: 0,
        sync: false,
        bufferProcessing: false,
        onwrite: [Function],
        writecb: null,
        writelen: 0,
        buffer: [],
        pendingcb: 0,
        prefinished: true,
        errorEmitted: false },
     writable: true,
     allowHalfOpen: true,
     _options: { objectMode: true },
     _wrapOptions: { objectMode: true },
     _streams: [ [Object] ],
     length: 1,
     label: 'deps' } }