added missing page_nav on forks page

rhodecode/templates/forks/fork.html

@@ -9,6 +9,9
     ${_('Fork')}
 </%def>
 
+<%def name="page_nav()">
+    ${self.menu('repositories')}
+</%def>
 <%def name="main()">
 ${self.context_bar('showforks')}
 <div class="box">