Update to a newer package snapshot

[fingolfin]

We are currently still using the packages intended for GAP 4.11.1, which are pretty old now. Unless GAP 4.12 is released very soon (which doesn't seem super likely to me right now, sadly) it would be good to update to a newer version of the GAP package distribution... (Or, of course, finally switch away from using that and instead completing and using the work started in https://github.com/oscar-system/GAP_pkg)