Set PEP440 compatible version string

[afrendeiro]

To build wheels for cytomine-python-client a PEP 440-compatible version string is needed. The current 'x.x.x' string in setup.py does not comply with this.
Please consider automatic versioning for example with https://github.com/pypa/setuptools_scm.

[waliens]

Hello @afrendeiro
Thank you for your comment. Could you share with us why you need to build the client yourself ? Recently, we have started to publish new versions of our client on PyPI so you might not need to rebuild it manually.