This PR allows to choose arbitrary ports for HTTP and HTTPS instead of 80 and 443.

While it does not change anything in the way ports can be mapped to host using native Docker capabilities, it fixes the "invalid" X-Forwarded-Port when the port on which nginx listens to is different from the one it is mapped - and accessed by clients - on the host.

Typical usage in docker-compose (here with the custom ports 1080 and 10443):

  reverse-proxy:
    image: jwilder/nginx-proxy
    ports:
      - "1080:1080"
      - "10443:10443"
    environment:
      HTTP_PORT: "1080"
      HTTPS_PORT: "10443"
    volumes:
      - /var/run/docker.sock:/tmp/docker.sock:ro

I'm open to suggestions.
Thanks for your amazing work on this image, it helps a lot.

Regards,