Run tox via python -m

.gitlab-ci.yml

@@ -24,7 +24,7 @@ test:
     - pip install tox  # you can also use tox
     - pip install --editable ".[test]"
     - python -c "import combo"
-    - tox -e py
+    - python -m tox -e py
 
 
 #before_script: