pipeline: install black via pipenv

Author: fphammerle

.github/workflows/python.yml

@@ -24,9 +24,12 @@ jobs:
     - uses: actions/setup-python@v1
       with:
         python-version: ${{ matrix.python-version }}
-    - run: pip install black==19.10b0
-    - run: pip freeze
-    - run: black --check .
+    - run: pip install --upgrade pipenv==2020.8.13
+    - run: pipenv install --python "$PYTHON_VERSION" --deploy --dev
+      env:
+        PYTHON_VERSION: ${{ matrix.python-version }}
+    - run: pipenv graph
+    - run: pipenv run black --check .
   tests:
     runs-on: ubuntu-18.04
     strategy:

Pipfile

@@ -15,7 +15,7 @@ numpy = "<1.19.0"
 [dev-packages]
 # black requires python>=3.6
 # https://github.com/psf/black/commit/e74117f172e29e8a980e2c9de929ad50d3769150#diff-2eeaed663bd0d25b7e608891384b7298R51
-#black = "==19.10b0"
+black = {version = "==20.8b1", markers = "python_version >= '3.6'"}
 pylint = "*"
 pylint-import-requirements = "*"
 #pytest = "*"