Add environment variable to disable nginx access log

[snoek09]

Problem

I'd like to be able to easily turn off nginx access logs as they clutter current logs with Laravel logs also being logged to stdout.

Also see #94

Solution

Add a NGINX_ACCESS_LOG environment variable and default it to /dev/stdout main which is the value currently set in /etc/nginx/nginx.conf.

Also mentioned here #94 (reply in thread)