`mypy` somehow fails when run on Python-3.9.0a5 ``` src/aapns/connection.py:36: error: syntax error in type comment ``` I'm pretty sure it worked with Python-3.9.0a4 and it works with Python-3.8.2: ``` src/aapns/connection.py:36: error: "list" is not subscriptable, use "typing.List" instead ```