docs: correct default site example

This handles ipv4 and ipv6.

[ci skip]

docs/configuration/domains.md

@@ -121,7 +121,9 @@ Create the file at `/etc/nginx/conf.d/00-default-vhost.conf`:
 
 ```nginx
 server {
+    listen 80 default_server;
     listen [::]:80 default_server;
+
     server_name _;
     access_log off;
     return 410;
@@ -137,6 +139,7 @@ server {
 # be copied into /etc/nginx/ssl/ folder.
 #
 # server {
+#     listen 443 ssl;
 #     listen [::]:443 ssl;
 #     server_name _;
 #     ssl_certificate /etc/nginx/ssl/cert.crt;