Update header.html

Author: hazzik

_includes/header.html

@@ -17,7 +17,7 @@ <h1 class="CommonHeaderTitle">NHibernate</h1>
         <li><a href="https://github.com/nhibernate/nhibernate.github.io/wiki">Uncyclos <i class="fa fa-external-link"></i></a></li>
         <li><a {% if page.url == '/groups.html' %} class="Selected" {% endif %} href="/groups.html">Groups</a></li>
         <li><a {% if page.url == '/doc/index.html' %} class="Selected" {% endif %} href="/doc/index.html">Documentation</a></li>
-        <li><a href="http://nhibernate.jira.com/">Issue tracker <i class="fa fa-external-link"></i></a></li>
+        <li><a href="https://github.com/nhibernate/nhibernate-core/issues">Issue tracker <i class="fa fa-external-link"></i></a></li>
         <li><a href="https://github.com/nhibernate/nhibernate-core">Source Code <i class="fa fa-external-link"></i></a></li>
       </ul>
       <div style="clear: both;"></div>