Add missing IPv6 "ssl" keyword in nginx config examples (#1854)

Signed-off-by: Arnaud Venturi <git@toadjaune.eu>

docs/nginx/monolith-sample.conf

@@ -1,6 +1,6 @@
 server {
     listen 443 ssl; # IPv4
-    listen [::]:443; # IPv6
+    listen [::]:443 ssl; # IPv6
     server_name my.hostname.com;
 
     ssl_certificate /path/to/fullchain.pem;

docs/nginx/polylith-sample.conf

@@ -1,6 +1,6 @@
 server {
     listen 443 ssl; # IPv4
-    listen [::]:443; # IPv6
+    listen [::]:443 ssl; # IPv6
     server_name my.hostname.com;
 
     ssl_certificate /path/to/fullchain.pem;