fixed icheck-bootstrap docs link in demo

pages/forms/advanced.html

@@ -1307,7 +1307,7 @@
               </div>
               <!-- /.card-body -->
               <div class="card-footer">
-                Many more skins available. <a href="http://fronteed.com/iCheck/">Documentation</a>
+                Many more skins available. <a href="https://bantikyan.github.io/icheck-bootstrap/">Documentation</a>
               </div>
             </div>
             <!-- /.card -->