drop python 3.7 and 3.8

[kushalkolar]

The latest ipython drops support for python 3.8 as per NEP 29: https://ipython.readthedocs.io/en/stable/whatsnew/version8.html#ipython-8-13

I thought a version bump would be appropriate too since it's a python version and not dep version change, but feel free to change :)

[almarklein]

Thanks!