setup.cfg: let python-tag mirror python_requires
setup.cfg: let python-tag mirror python_requires

In order to generate a wheel in accordance with PEP 425 to restrict the
minimum required version of Python (3.6), the `python-tag` bdist_wheel
option needs to be specified so the wheel gets tagged properly.

Before:
	zipp-x.x.x-py3-none-any.whl
After:
	zipp-x.x.x-py36-none-any.whl

Signed-off-by: Vincent Fazio <ea26f9afc292f20966dd0e9d80dfba2051b837ac@xes-inc.com>

jazzband/inflect,jaraco/jaraco.path,jaraco/backports.functools_lru_cache,jaraco/calendra,yougov/pmxbot,jaraco/hgtools,jaraco/irc,pwdyson/inflect.py,jaraco/jaraco.logging,jaraco/jaraco.stream,jaraco/jaraco.functools,pytest-dev/pytest-runner,jaraco/portend,yougov/pmxbot,jaraco/zipp,jaraco/jaraco.classes,yougov/pmxbot,jaraco/jaraco.itertools,jaraco/jaraco.collections,jaraco/keyring,jaraco/tempora,python/importlib_metadata,jaraco/jaraco.context,jaraco/jaraco.text