Fix travis

.travis.yml

@@ -3,7 +3,7 @@ python:
   - "3.7"
 install:
   - pip install -r requirements.txt
-  - pip install flake8 codecov coverage
+  - pip install black codecov coverage
 script:
   - black --check entrypoint.py sphinx_action tests
   - coverage run --omit="*/tests*" -m unittest