message: fix playlist translation in sidebar
diff: </div>
  <div v-if="!collections.length">
  - <div class="alert fill-gray">
  - <translate>library.nav.no_playlists_html</translate>
  + <div class="alert fill-gray" v-translate>
  + library.nav.no_playlists_html
  </div>
  </div>
  