Fix gitlab link in sidebar

Minor, but since I spotted it, might as well fix

_includes/sidebar.html

@@ -21,7 +21,7 @@
         <a href="{{ site.baseurl }}/atom.xml"><img class="icon" src="{{ site.baseurl }}/public/feed_w.png" alt="atom feed"/>,</a>
         <!-- <a href="https://twitter.com/{{ site.author.twitter }}"><img class="icon"
 	     src="{{ site.baseurl }}/public/twitter_w.png" alt="twitter"/></a> -->
-        <a href="https://gitlab.com/{{ site.repository_url }}"><img class="icon" src="{{ site.baseurl }}/public/gitlab.png" alt="gitlab"/>.</a>
+        <a href="{{ site.repository_url }}"><img class="icon" src="{{ site.baseurl }}/public/gitlab.png" alt="gitlab"/>.</a>
       </span><br/>
 
       <a class="sidebar-nav-item" href="{{site.repository_url}}/edit/master/{% if page.source %}{{ page.source }}{%