Fix python test failure using virtualenv<20.0.0#641

Merged

ancasarb merged 1 commit intocombust:masterfrom lucagiovagnoli:luca/fix-virtualenv-python-tests-bug-640

Feb 19, 2020

+40-12

Commits on Feb 13, 2020

Moving to Travis stages because python various virtualenv were not being run with the correct python version - pin virtualenv to be <20.0.0 because of pypa/virtualenv#1551 - use different distro fo…
lucagiovagnoli
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