pipenv: remove black to restore compatibility with python3.5

.github/workflows/python-code-format.yml

@@ -0,0 +1,20 @@
+name: code format
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-18.04
+    steps:
+    - uses: actions/checkout@v1
+    - uses: actions/setup-python@v1
+      with:
+        # black requires python>=3.6
+        # https://github.com/psf/black/commit/e74117f172e29e8a980e2c9de929ad50d3769150#diff-2eeaed663bd0d25b7e608891384b7298R51
+        python-version: 3.8
+    - run: python --version
+    - run: pip install --upgrade black==19.10b0
+    - run: pip freeze
+    - run: black --check .

.github/workflows/python.yml

@@ -42,7 +42,6 @@ jobs:
     - run: pipenv run pylint --disable=parse-error tests/*
     - run: pipenv run mypy ical2vdir tests
     - run: pipenv run pytest --cov=ical2vdir --cov-report=term-missing --cov-fail-under=100
-    - run: pipenv run black --check .
     # >=1.9.0 to detect branch name
     # https://github.com/coveralls-clients/coveralls-python/pull/207
     # https://github.com/coverallsapp/github-action/issues/4#issuecomment-547036866

Pipfile

@@ -5,7 +5,9 @@ name = "pypi"
 
 [dev-packages]
 ical2vdir = {editable = true,path = "."}
-black = "==19.10b0"
+# black requires python>=3.6
+# https://github.com/psf/black/commit/e74117f172e29e8a980e2c9de929ad50d3769150#diff-2eeaed663bd0d25b7e608891384b7298R51
+#black = "==19.10b0"
 mypy = "*"
 pylint = "*"
 pylint-import-requirements = "*"