message: fix python invocation when using ubuntu 18.04
diff: @@ -15,7 +15,7 @@ jobs:
  name: install dependencies
  command: |
  apt-get update && apt-get install -y clang-format-8 python3.7
  - python3 -m venv venv
  + python3.7 -m venv venv
  . venv/bin/activate
  ./scripts/setup.sh
  