v2.2.0

Summary:
Quick fix for annotations error in earlier versions of Python3.

Itemized Changes:

• fix: Python 3.9 annotations error by @robbibt in https://github.com/tsutterley/pyTMD/pull/373

Full Changelog: https://github.com/tsutterley/pyTMD/compare/2.1.9...2.2.0