Inconsistent type for URL across SBKAlbum, SBKTrack and SBKArtist

[Rob In der Maur]

For SBKAlbum, URL is of type String?, for the others of type URL?

[Tomás Martins]

Hi @ridmaur, thanks for opening this issue and sorry for taking a while to get back to you. I've released a new release 1.0.3 that updates the URL types from some public models to URL, to be inline with the rest of them