fix ci

.github/workflows/formatting.yml

@@ -11,6 +11,8 @@ jobs:
         uses: actions/checkout@v2
       - name: Setup Python
         uses: actions/setup-python@v1
+        with:
+          python-version: "3.7"
       - name: Install dependencies
         run: |
           pip install black flake8

.github/workflows/testing.yml

@@ -12,7 +12,7 @@ jobs:
     steps:
     - uses: actions/setup-python@v2
       with:
-        python-version: "3.x"
+        python-version: "3.7"
     - uses: actions/checkout@v2
     - name: Lint with flake8
       run: |
@@ -34,6 +34,9 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: ${{ matrix.python-version }}
+    - name: Update
+      run: |
+        sudo apt update
     - name: Install CGAL 5
       run: |
         sudo apt install -y libcgal-dev

pyproject.toml

@@ -1,3 +1,6 @@
 [build-system]
 requires = ["setuptools>=42", "wheel", "pybind11>=2.6.0", "versioneer-518"]
 build-backend = "setuptools.build_meta"
+
+[tool.black]
+target-version = ['py37']