nipxkgs manifests list "git" origins as "urls"

It's currently worked around in the lister [0] but the surest fix would be that the manifest corrects it itself.

There is already a 2,5 year old task [1] about this in the upstream repository. I've pinged it (and also tried to have a look at it but i can't that fails... [2], i've opened another issue about it)