setup.cfg: bump version to 2.3.3

[simondeziel]

Procedure:

$ python3 setup.py sdist
...
$ python3 setup.py bdist_wheel
...
$ python3 -m twine check --strict dist/*
Checking dist/pylxd-2.3.3-py3-none-any.whl: PASSED
Checking dist/pylxd-2.3.3.tar.gz: PASSED
# upload to testpypi
$ python3 -m twine upload --repository pylxd-testpypi dist/*
Uploading distributions to https://test.pypi.org/legacy/
Uploading pylxd-2.3.3-py3-none-any.whl
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 102.2/102.2 kB • 00:04 • 173.0 MB/s
Uploading pylxd-2.3.3.tar.gz
100% ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 75.5/75.5 kB • 00:00 • 163.9 MB/s

View at:
https://test.pypi.org/project/pylxd/2.3.3/

The test upload is available at https://test.pypi.org/project/pylxd/2.3.3/