Use new PyPI attribute to detect CI downloads

[joelostblom]

The ability to differentiate automated installs from manual ones was recently added in pip and PyPI; see pypa/pip#5499 and pypi/linehaul-cloud-function#9 for details. It would be great to have this functionality available on pypistats.org as well. A similar tool that added this recently was pypinfo and the approach can be seen here in case it is helpful ofek/pypinfo#157