How to compile and configure BoringSSL with nginx to support TLSv1.3

I saw a blog on your site showig that [Cloudflare is using BoringSSL](https://blog.cloudflare.com/make-ssl-boring-again/) and issue [#78](https://github.com/cloudflare/sslconfig/issues/78) also prove the usage of BoringSSL.

>As it happens, BoringSSL has supported TLS 1.3 for quite a long time (it was one the first open source SSL implementations to work on this feature), so now all of our edge SSL traffic (including TLS 1.3 connections) is handled by the same system, with no duplication, no added complexity, and no increased latency. Yay!

However I compiled BoringSSL with nginx 1.13.7 using configuration `--with-openssl=/path/to/boringssl --with-openssl-opt=enable-tls1_3` and it could not support TLSv1.3 Draft18 (like Cloudflare does).

BoringSSL supported TLSv1.3 draft18 since [this commit](https://github.com/google/boringssl/commit/a833c357edae4eb7f47b9808bf744bd9bb0df18d) but I could not find an wiki or an explanation about how to compile and configure BoringSSL with nginx to support TLSv1.3 draft18.