Added noopener to external link

Security update. More info can be found on https://developers.google.com/web/tools/lighthouse/audits/noopener.

src/templates/default/main/menu.tpl.html

@@ -4,7 +4,7 @@
 	  <li class="{{ item.active }}"><a href="{{ item.url|raw }}">{{ item.label }}</a></li>
 	  {% endfor %}
 	  <li id="nav_option_help">
-		  <a href="http://www.phpservermonitor.org/support" target="_blank">{{ label_help }}</a>
+		  <a href="http://www.phpservermonitor.org/support" target="_blank" rel="noopener">{{ label_help }}</a>
 	  </li>
   </ul>
   <ul class="nav pull-right">