Test with Python 3.8

[adamchainz]

No description provided.

[adamchainz]

Currently seeing a breakage inside Pytest:

  File "/Users/chainz/Documents/Projects/scout_apm_python/.tox/py38-django22/lib/python3.8/site-packages/_pytest/config/__init__.py", line 631, in _iter_rewritable_modules
    for fn in package_files:
  File "/Users/chainz/Documents/Projects/scout_apm_python/.tox/py38-django22/lib/python3.8/site-packages/_pytest/config/__init__.py", line 848, in <genexpr>
    package_files = (
  File "/Users/chainz/Documents/Projects/scout_apm_python/.tox/py38-django22/lib/python3.8/importlib/metadata/__init__.py", line 175, in <genexpr>
    resolver()
  File "<frozen importlib._bootstrap_external>", line 1383, in find_distributions
AttributeError: type object 'DistributionFinder' has no attribute 'Context'

[adamchainz]

Currently seeing a problem using Black on Python 3.8 - switching to it uses the newer pickle which causes the cache to break

Waiting for the upcoming release that includes the fix for the issue: psf/black#875

[adamchainz]

Black was released on Monday, the cache problem has been fixed: https://pypi.org/project/black/#history