Update nginx install script

[hyanwong]

When running sudo ./install-nginx.sh, we get some deprecation errors

nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead in /usr/local/etc/nginx/conf.d/a.onezoom.org.conf:14
nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead in /usr/local/etc/nginx/conf.d/imagesa.onezoom.org.conf:5
nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead in /usr/local/etc/nginx/conf.d/onezoom.org.conf:3
nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead in /usr/local/etc/nginx/conf.d/www.onezoom.org.conf:25
nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead in /usr/local/etc/nginx/conf.d/zz_images.onezoom.org.conf:5
nginx: the configuration file /usr/local/etc/nginx/nginx.conf syntax is ok

[hyanwong]

Looks like we need to go from

listen 443 ssl;

to

listen 443 ssl;
http2 on;

[hyanwong]

I'll do this once we have the new beta.onezoom.org server running