Log Message:
py-priority: update to 2.0.0.

2.0.0 (2021-06-27)
------------------

**API Changes**

- Python 3.6 is the minimal support Python version.
- Support for Python 3.7 has been added.
- Support for Python 3.8 has been added.
- Support for Python 3.9 has been added.
- Support for Python 2.7 has been removed.
- Support for Python 3.3 has been removed.
- Support for Python 3.4 has been removed.
- Support for Python 3.5 has been removed.
- Support for PyPy (Python 2.7 compatible) has been removed.
- Add type hints throughout and support PEP 561 via a py.typed
  file. This should allow projects to type check their usage of this dependency.
- Throw ``TypeError`` when creating a priority tree with a ``maximum_streams``
  value that is not an integer.
- Throw ``ValueError`` when creating a priority tree with a ``maximum_streams``
  value that is not a positive integer.