Test created projects on Python 3.7
We currently test using Python 2.7 and 3.6. However, the latest version of Python is 3.7, so this will be what most people will download by default.
So far I have found out that scikit-surgeryvtk doesn't work on 3.7, as there aren't the necessary wheels for PySide2 or vtk. I think opencv does have a 3.7 wheel, but haven't tested it. There isn't anything we can do about these external dependencies at the moment, but we should at least know about any issues that arise.