`updateScript` lets us update packages automatically.
For packages that are hosted on the gnome mirror it's very easy to add
that. Inspired by https://github.com/NixOS/nixpkgs/issues/36150
I'm not updating to the 2.x version yet, because the only dependee of
this package is 'shutter' (which I'm about to package) and it doesn't
support 2.x.