appveyor: require py3 to pass
appveyor: require py3 to pass

Signed-off-by: Ruslan Kuprieiev <e9bfb2c543dd33934bcff71879b108246996b567@iterative.ai>

efiop/dvc,dmpetrov/dataversioncontrol,efiop/dvc,dmpetrov/dataversioncontrol