message: refactor(options): add shortkey entry for Chrome
diff: <label class="checkbox-inline">
  <input type="checkbox" v-model="pdfSniff"> {{ $t('opt:pdf_sniff') }}
  </label>
  + <button v-if="isChrome" type="button" class="btn btn-default btn-xs" @click="openShortkey">{{ $t('opt:set_shortkey') }}</button>
  </div>
  </div>
  <div class="opt-item__description-wrap">
  </template>
  <script>
  +import { openURL } from '@/_helpers/browser-api'
  +
  export default {
  store: {
  active: 'config.active',
  pdfSniff: 'config.pdfSniff',
  },
  + data () {
  + return {
  + // @todo wait for firefox https://bugzilla.mozilla.org/show_bug.cgi?id=1303384
  + isChrome: navigator.userAgent.indexOf('Chrome') !== -1
  + }
  + },
  + methods: {
  + openShortkey () {
  + openURL('chrome://extensions/shortcuts')
  + }
  + },
  }
  </script>
  