Fix deprecated setting in nginx configuration

[beathorst]

After updating nginx we get deprecation warnings.

nginx -t
nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead in etc/nginx/nginx.conf :15
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

It is described here
https://www.nginx.com/blog/nginx-plus-r30-released/

Change this:

listen 443 ssl http2;
To this:

listen 443 ssl;
http2 on;