Drop support for EOL Python 2

[hugovk]

Fixes #115.

[di]

If I understand #114 correctly, we can also make this change:

- check-manifest --ignore 'tox.ini,tests,tests/**'
+ check-manifest --ignore 'tox.ini,tests/**'

[hugovk]

If I understand #114 correctly, we can also make this change:

- check-manifest --ignore 'tox.ini,tests,tests/**'
+ check-manifest --ignore 'tox.ini,tests/**'

Updated in a4117c8.

With check-manifest 0.41, the former passes and the latter fails:

$ check-manifest --version
check-manifest version 0.41
$ check-manifest --ignore 'tox.ini,tests,tests/**'
lists of files in version control and sdist match
$ check-manifest --ignore 'tox.ini,tests/**'
lists of files in version control and sdist do not match!
missing from sdist:
  tests
$

With check-manifest 0.42, both pass:

$ check-manifest --version
check-manifest version 0.42
$ check-manifest --ignore 'tox.ini,tests,tests/**'
lists of files in version control and sdist match
$ check-manifest --ignore 'tox.ini,tests/**'
lists of files in version control and sdist match

[di]

Thanks all!