Replace partner-callout with contributor-callout

Co-authored-by: Sarah Schneider <sarahs@users.noreply.github.com>

Author: Steve Winton

includes/article.html

@@ -21,7 +21,7 @@ <h1 class="border-bottom-0">{{ page.title }}</h1>
       </div>
 
       {% if page.contributor %}
-        <div class="partner-callout border rounded-1 mb-4 p-3 border-blue bg-blue-light f5">
+        <div class="contributor-callout border rounded-1 mb-4 p-3 border-blue bg-blue-light f5">
           <p>This page is kindly contributed and maintained by <a href="{{ page.contributor.URL }}" rel="nofollow">{{ page.contributor.name }}</a>.</p>
         </div>
       {% endif %}