script: add webui ipv6 listen directive (fixes #158)

resources/klipper_webui_nginx.cfg

@@ -2,6 +2,7 @@
 
 server {
     listen 80;
+    listen [::]:80;
 
     access_log /var/log/nginx/<<UI>>-access.log;
     error_log /var/log/nginx/<<UI>>-error.log;