Use 'python3' instead of 'python3.6' on tox
Use 'python3' instead of 'python3.6' on tox

This allows us to use python3.7+ to use tox

The-Compiler/pytest,Akasurde/pytest,alfredodeza/pytest,The-Compiler/pytest,pytest-dev/pytest,RonnyPfannschmidt/pytest,markshao/pytest,nicoddemus/pytest,nicoddemus/pytest