tox < 3.0.0; python_version == '3.3'
tox; python_version != '3.3'
virtualenv == 15.2.0; python_version == '3.3'

tox < 3.0.0; python_version == '3.3'
tox < 4.0.0; implementation_name == 'pypy'
tox; python_version != '3.3' and implementation_name != 'pypy'
virtualenv == 15.2.0; python_version == '3.3'

Use older tox for the pypy python
Use older tox for the pypy python
