add commata between author names

templates/blog/author_media.html

 <div class="columns">
-  <div class="column">
+  <div class="column is-two-fifths">
 {% set authors_data = load_data(path="authors.json") -%}
 {% for author in post.authors -%}
     <figure class="image is-48x48 is-inline-block" style="margin-right:  -30px;">
@@ -17,10 +17,16 @@
 {% endfor %}
   </div>
   <ul class="column is-three-fifths">
+    <div class="title is-5">
 {% for author in post.authors -%}
-    <li class="title is-5 is-inline mr-3">
+      <p class="is-inline">
       {{ authors_data[author].display_name }}
-    </li>
+        {% if not loop.last %}
+        ,
+        {% endif %}
+      </p>
 {% endfor %}
+    </div>
   </ul>
 </div>
+