use site time for now

Author: ryanphuang

_includes/footer.html

@@ -5,7 +5,7 @@
     <p class="footer-text m-0 col-lg-8 col-md-12">
       Copyright &copy; OrderLab 2017-<script>
  document.write(new Date().getFullYear());
-      </script> All rights reserved. | Last updated {{ page.last_modified_at }}.
+      </script> All rights reserved. | Last updated {{ site.time }}.
     </p>
   </div>
 </div>