- Add the 'gitUpdater' helper function to update git based packages, using the
'genericUpdater' function.
- Rework argument passing to the `list-git-tags' and 'list-archive-two-level-versions' scripts.
- Replace 'genericUpdater' plus 'list-git-tags' by 'gitUpdater'
The script was broken when nixpkgs-unstable was in NIX_PATH, which
resulted in nix 2.5 being used instead of 2.3.
It now works with nixpkgs-unstable and `nixpkgs-21.*`.
It's now sufficient to run a single script (btcpayserver/update.sh) to
update btcpayserver. This simplifies maintenance.
nbxplorer is a strict dependency of btcpayserver.
