Enable TLS v1.3 by default in NGINX

Now that we're shipping OpenSSL v1.1.1 and TLS v1.3 is becoming used more frequently, let's enable it by default.

More details:

• https://wiki.openssl.org/index.php/TLS1.3
• https://blog.cloudflare.com/introducing-tls-1-3/

When enabling it on Firefox, I confirmed TLS v1.3 is showing:

Closes #4526 (closed)