Fix CD and install issues

[redeboer]

There are a few bugs with the deployment:

• For some reason, the CD job does not run anymore upon creating a release
• The notebooks don't work anymore on Google Colab. When running pip install expertsystem[doc], one gets a PEP517 error

  Collecting expertsystem[doc]
    Downloading https://files.pythonhosted.org/packages/39/a0/071521c5b2dc67aca80ad925634b29d77e902a54ffe8a909d25fe7899c89/expertsystem-0.6.2.tar.gz (125kB)
      |████████████████████████████████| 133kB 2.7MB/s 
    Installing build dependencies ... done
    Getting requirements to build wheel ... done
      Preparing wheel metadata ... error
  ERROR: Command errored out with exit status 1: /usr/bin/python3 /usr/local/lib/python3.6/dist-packages/pip/_vendor/pep517/_in_process.py prepare_metadata_for_build_wheel /tmp/tmpmt7g_nci Check the logs for full command output.
  

  I think this can be solved by building a wheel

[redeboer]

Update: installing the expertsystem on Google Colab is again possible.