Update docker nginx.conf to enable ipv6

I'm having connectivity issues in my dual stack environment and this seems to fixes them.

.docker/nginx.conf

@@ -1,11 +1,12 @@
 server {
   listen 80;
-
+  listen [::]:80;
+
   location / {
     root /usr/share/nginx/html;
     index index.html index.htm;
     try_files $uri $uri/ /index.html =404;
   }
 
   include /etc/nginx/extra-conf.d/*.conf;
-}
+}