Only raise a warning, not an error for privileged ports

[matt-allan]

On MacOS, on Linux if using authbind, and maybe other cases I don't know about, you don't actually need to use sudo to bind to ports < 1024. However when I try to bind to port 80, Node Foreman raises an error. If I prevent Node Foreman from throwing an error it works fine.

Since we can't detect if this system will or will not require sudo we can just raise a warning instead. We could omit the warning entirely but it might be harder to diagnose the issue if you your system does require sudo?

The use case for me is running a local webserver on port 80 and not having to enter a sudo password every time or unnecessarily elevate permissions.

I've been working around the issue by using a different environment variable to pass the PORT through, but that's pretty confusing for everyone else on the team 😁

I'm having trouble finding a reference for the MacOS guidelines; this is the best I could find: https://news.ycombinator.com/item?id=18302380