Patch 1 (#7017)

* listen on IPv6 as well as IPv4

Added a line to also listen on IPv6. Without this line, I was unable to connect to my freshly installed mattermost server, because IPv6 seemed to be automatically chosen, but nginx didn't listen on it.

* removed ssl directive

the ssl directive is deprecated and "listen ... ssl" should now be used, according to nginx. removing the statement "ssl on;" doesn't affect behaviour, because ssl is already enabled by the listen directive.

source/install/config-proxy-nginx.rst

@@ -40,11 +40,11 @@ SSL and HTTP/2 with server push are enabled in the provided configuration exampl
 
     server {
        listen 443 ssl http2;
+       listen [::]:443 ssl http2;
        server_name    mattermost.example.com;
 
        http2_push_preload on; # Enable HTTP/2 Server Push
 
-       ssl on;
        ssl_certificate /etc/letsencrypt/live/{domain-name}/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/{domain-name}/privkey.pem;
        ssl_session_timeout 1d;