Building polybar requires sphinx.domains.changeset, which is not available in sphinx 1.6.7. Sphinx 1.6.7 is installed when using either apt install python3-sphinx or pip install -U sphinx on Ubuntu 18.04.

As these commands are suggested in the corresponding entry in your wiki, you should mentioned this problem there. Ideally, you could also add a brief guideline for installing a more recent version of sphinx (e. g. by using anaconda).