Use same version of tox on travis.
#!/usr/bin/env bash
if [ "${TASK}" = 'compilepy3 ci-py3-unit' ] || [ "${TASK}" = 'ci-py3-integration' ]; then
- pip install "tox==3.5.2"
+ pip install "tox==3.7.0"
# Install runners
. virtualenv/bin/activate
