Support for pygit2 1.2 and libgit2 1.0.0

[hexagonrecursion]

• Fedora 32 ships libgit2 1.0.0.
• According to the change log support for libgit2 1.0.0 was only added in pygit2 1.2.0
• gitfs requires pygit2==0.28.2
  => I can't install gitfs. :(