travis: use pyenv shell
travis: use pyenv shell

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

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