packaging: upgrade packages in Windows environment
I ran pip-compile -U to update all packages to latest versions.
I did this so the Windows environment is more modern.
dulwich 0.20 dropped support for Python 2.7. Rather than add
yet another requirements.txt file, I decided to just pin at an
older release to minimize complexity.
Differential Revision: https://phab.mercurial-scm.org/D9187