Upgrade to hgvs 2.0.0a0

[korikuzma]

The latest release of hgvs (which was 3 years since the last release) is causing CI tests to fail in #578 . I haven't really looked at these in detail, but we should resolve the tests and/or update code to reflect these changes.

[korikuzma]

https://pypi.org/project/hgvs/2.0.0a0/

[korikuzma]

I'm assuming this one will not result in a breaking change, but I would like to see it prioritized to get in by the time we make a v3 release.