Dependency issues in beta release

The latest beta release (2.10.0b0) can't be installed with pipenv because the hash on pyyaml doesn't match.

If I manually pip install pyyaml in the virtual environment, I can then run pipenv install --dev successfully. I think this means some hashes were out of date or possibly wrong.

I'm not quite sure why this should happen: I don't expect old packages would disappear or change on PyPI or PiWheels, but it's possible that a broken lockfile was generated (e.g. on a non-RPi platform) and that's the problem.