Changes with nginx 1.15.6 06 Nov 2018
*) Security: when using HTTP/2 a client might cause excessive memory consumption (CVE-2018-16843) and CPU usage (CVE-2018-16844).
*) Security: processing of a specially crafted mp4 file with the ngx_http_mp4_module might result in worker process memory disclosure (CVE-2018-16845).
*) Feature: the "proxy_socket_keepalive", "fastcgi_socket_keepalive", "grpc_socket_keepalive", "memcached_socket_keepalive", "scgi_socket_keepalive", and "uwsgi_socket_keepalive" directives.
*) Bugfix: if nginx was built with OpenSSL 1.1.0 and used with OpenSSL 1.1.1, the TLS 1.3 protocol was always enabled.
*) Bugfix: working with gRPC backends might result in excessive memory consumption.