Update ipynbtests to (maybe) work with Py 3.8/3.9
Update ipynbtests to (maybe) work with Py 3.8/3.9

dwhswenson/openpathsampling,dwhswenson/openpathsampling,dwhswenson/openpathsampling,choderalab/openpathsampling,openpathsampling/openpathsampling,choderalab/openpathsampling,openpathsampling/openpathsampling,dwhswenson/openpathsampling,openpathsampling/openpathsampling,choderalab/openpathsampling,openpathsampling/openpathsampling