Fix travis build with python3.6 (spiral-project#734)

Upgrade pip **and** virtualenv, as mentioned in https://travis-ci.community/t/pip-install-cryptography-fails-on-py36/11233/4 Tox is building its own virtualenv, so the image from TravisCI might not be enough for pip to find the wheel.
TomRoussel · Apr 6, 2021 · 51f3d2c · 51f3d2c
1 parent 706efcc
commit 51f3d2c
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/.travis.yml b/.travis.yml
@@ -6,5 +6,7 @@ python:
   - "3.8"
   - "3.9"
 script: tox
+before_install:
+  - python -m pip install --upgrade pip virtualenv
 install:
   - pip install tox-travis