improve HTTPS validation

[ghost]

If you are running pump.io behind a reverse proxy, you really don't need to set up the SSL key/cert because you can set up directly for example in NGINX, so we should improve that validation or add and options like useHTTPS or check if the port is 443, because if the server run with 443 without ssl cert it still send the request over http and will get invalid signature error.

https://github.com/pump-io/pump.io/blob/master/lib/app.js#L201

Related: #1699