Interactive credential authentication shouldn't use 127.0.0.1 as redirect URL

[chriscn]

When setting up credentials with go-librespot, and clicking the link you're redirected back to 127.0.0.1 which doesn't work well if you're running go-librespot on a headless Pi and signing in on your laptop.

It should instead use the device's IP address.

[devgianlu]

Spotify restricts the callback to 127.0.0.1 or [::1], anything else gets redirect_uri: Not matching configuration