Update "xcb-util-cursor-git" upstream url

[andrei-korshikov]

@eclairevoyant Thank you for maintaining!

I would suggest to change Upstream URL to https://gitlab.freedesktop.org/xorg/lib/libxcb-cursor

The reasons:

• this is the place where the development is going on, I think it's important for -git package
• there is no obvious way to go from https://xcb.freedesktop.org/ (the current Upstream URL) to the gitlab repo

So, formally the current upstream URL is correct, but it is useless in practice, when one wants to find current issues for the project.

Another variant: leave Upstream URL as it is, but change Source to https://gitlab.freedesktop.org/xorg/lib/libxcb-cursor.git

Or do both) See the README, they use these very links.