AttributeError on updating the database

[noyainrain]

Application.update() fails with the following error:

Traceback (most recent call last):
  File ".venv39/lib/python3.9/site-packages/tornado/testing.py", line 268, in _callTestMethod
    result = method()
  File ".venv39/lib/python3.9/site-packages/tornado/testing.py", line 604, in post_coroutine
    return self.io_loop.run_sync(
  File ".venv39/lib/python3.9/site-packages/tornado/ioloop.py", line 547, in run_sync
    return future_cell["future"].result()
  File "micro/tests/test_micro.py", line 121, in test_update_db_fresh
    await app.update()
  File "micro/micro.py", line 230, in update
    self._generate_push_vapid_keys()) # type: ignore
  File "micro/micro.py", line 472, in _generate_push_vapid_keys
    b64urlencode(vapid.public_key.public_numbers().encode_point()))
AttributeError: 'cryptography.hazmat.primitives.asymmetric.ec.Ellip' object has no attribute 'encode_point'

[noyainrain]

This has the same cause as #59:

1. The deprecated encode_point() is called when generating VAPID keys