maybe repository is a reserved variable name

_config.yml

@@ -25,7 +25,8 @@ author:
   email:               michael.kohlhase@fau.de
 #  twitter:             OpenMathSoc
 
-repository:    https://gl.kwarc.info/SIGMathLing/website
+repository_url:    https://gl.kwarc.info/SIGMathLing/website
+repository: SIGMathLing/website
 sources: 	     https://gl.kwarc.info/SIGMathLing/website#the-sources-of-the-sigmathling-web-site
 
 collections:

_includes/sidebar.html

@@ -23,7 +23,7 @@
         <a href="https://github.com/{{ site.github.owner_name }}"><img class="icon" src="{{ site.baseurl }}/public/gitlab.png" alt="github"/></a>
       </span><br/>
 
-      <a class="sidebar-nav-item" href="{{site.repository}}/edit/master/{% if page.source %}{{ page.source }}{%
+      <a class="sidebar-nav-item" href="{{site.repository_url}}/edit/master/{% if page.source %}{{ page.source }}{%
 					else %}{{ page.path }}{% endif %}">Edit this page</a>
       (<a class="sidebar-nav-item" href="{{ site.sources }}">HowTo</a>)<br/>