pkg-resources==0.0.0 in requirements.txt

[wooohoooo]

install fails on ubuntu 18.04,

ERROR: Could not find a version that satisfies the requirement pkg-resources==0.0.0 (from -r requirements.txt (line 17)) (from versions: none)
ERROR: No matching distribution found for pkg-resources==0.0.0 (from -r requirements.txt (line 17))

according to https://stackoverflow.com/questions/39577984/what-is-pkg-resources-0-0-0-in-output-of-pip-freeze-command (and successively via pypa/pip#4022) it's a quirk in Ubuntu providing wrong metadata and should be safe to remove.

Given the appearance of a few data sets related to COVID-19 it might be good to do that in order to decrease the threshold for using the model.

Thanks, keep up the awesome work!