Closes #6702: Update reference nginx config to support IPv6

contrib/nginx.conf

@@ -1,5 +1,5 @@
 server {
-    listen 443 ssl;
+    listen [::]:443 ssl ipv6only=off;
 
     # CHANGE THIS TO YOUR SERVER'S NAME
     server_name netbox.example.com;
@@ -23,7 +23,7 @@ server {
 
 server {
     # Redirect HTTP traffic to HTTPS
-    listen 80;
+    listen [::]:80 ipv6only=off;
     server_name _;
     return 301 https://$host$request_uri;
 }