tall må eksplisitt bli streng i router-link

src/components/SubArticle.vue

 <template>
   <li class="sub_article">
     <span class="sub_article_header">
-      <router-link :to="body.article_id"  @click.native="article_link_click(body)">
+      <router-link :to="'' + body.article_id"  @click.native="article_link_click(body)">
         {{body.lemmas[0]}}
       </router-link>
     </span>