Updated the footer link of coqdocjs

As the repo got probably moved to coq-community, the link should be
updated, although redirection works.

Author: motrellin

extra/footer.html

@@ -1,6 +1,6 @@
 </div>
 <div id="footer">
-  Generated by <a href="http://coq.inria.fr/">coqdoc</a> and improved with <a href="https://github.com/tebbi/coqdocjs">CoqdocJS</a>
+  Generated by <a href="http://coq.inria.fr/">coqdoc</a> and improved with <a href="https://github.com/coq-community/coqdocjs">CoqdocJS</a>
 </div>
 </div>
 </body>