Point libgit2 submodule to 0.21 maintenance branch

[ashleyblackmore]

Hey @uniphil, not sure if this is what you meant - I'm not super-familiar with submodules. Please let me know.

[uniphil]

Submodules are a bit tricky. the .gitmodules file doesn't actually tell git anything except where to find the remote for the repo. Once you've done git submodule init or update or whatever, git starts doing magic behind the scenes to track a specific commit hash for the submodule. blah. whatever. :)

I pushed a release called v0.21.libgitmaint.0 to pypi, which I think should work for you (fingers crossed!). Please re-open this if it doesn't work.

Also just a heads up that this won't stay up to date with new commits on the v0.21.maint branch of libgit2, since submodules only track a specific commit hash. We can roll out new maintenance tracking releases here if it updates and anyone needs the fixes.

[ashleyblackmore]

Thanks so much. It is working, I can't tell you how helpful this has been! :)