Include stable docs, use Apache URLs

Change-Id: Iadb5074e130d4a21b2af123aa405e9fc21a14aed
Reviewed-on: https://asterix-gerrit.ics.uci.edu/519
Reviewed-by: Till Westmann <tillw@apache.org>
diff --git a/_includes/nav_header.html b/_includes/nav_header.html
index c121456..5123fab 100644
--- a/_includes/nav_header.html
+++ b/_includes/nav_header.html
@@ -22,10 +22,10 @@
                 <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-expanded="false">Documentation<span class="caret"></span></a>
                 <ul class="dropdown-menu" role="menu">
                   <li class="dropdown-header">Stable release</li>
-                  <li><a href="{{ site.DOCS_BASE_URL }}/index.html">Documentation for {{ site.STABLE_VERSION }}<i class="fa fa-external-link fa-sm"></i></a></li>
+                  <li><a href="{{ site.DOCS_BASE_URL }}/{{ site.STABLE_VERSION }}/index.html">Documentation for {{ site.STABLE_VERSION }}<i class="fa fa-external-link fa-sm"></i></a></li>
                   <li class="divider"></li>
                   <li class="dropdown-header">Snapshot release</li>
-                  <li><a href="{{ site.UNSTABLE_DOCS_BASE_URL }}/index.html">Documentation for {{ site.UNSTABLE_VERSION }}  <i class="fa fa-external-link fa-sm"></i></a></li>
+                  <li><a href="{{ site.UNSTABLE_DOCS_BASE_URL }}index.html">Documentation for {{ site.UNSTABLE_VERSION }}  <i class="fa fa-external-link fa-sm"></i></a></li>
                 </ul>
               </li>
               <li><a href="{{ site.url }}about.html">About</a></li>