fixes vimium not giving retweet button a hint

src/components/retweet_button/retweet_button.vue

 <template>
   <div v-if="loggedIn">
     <template v-if="visibility !== 'private' && visibility !== 'direct'">
-      <i :class='classes' class='icon-retweet rt-active' v-on:click.prevent='retweet()'></i>
+      <i :class='classes' class='retweet-button icon-retweet rt-active' v-on:click.prevent='retweet()'></i>
       <span v-if='!hidePostStatsLocal && status.repeat_num > 0'>{{status.repeat_num}}</span>
     </template>
     <template v-else>