Update ci
Hi @arianna.renzini (and others) I started looking at the code coverage and noticed some issues with the CI/setup script.
This should fix those issues, the code coverage (the fraction of lines tested in the unit tests) is now reported by the CI.
I did hike the minimum python version in line with the numpy
deprecation schedule. Since it's still early days for this project, I think it's worth taking a somewhat hard line on it.