Drop Python 3.6 which reached EOL December 2021

.github/workflows/ci-build.yml

@@ -28,7 +28,7 @@ jobs:
 
     strategy:
       matrix:
-        python-version: ['3.6', '3.7', '3.8', '3.9']
+        python-version: ['3.7', '3.8', '3.9']
 
     name: Build with Python ${{ matrix.python-version }}
     steps:
@@ -52,10 +52,10 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@v2
-      - name: Set up Python 3.6
+      - name: Set up Python 3.8
         uses: actions/setup-python@v2
         with:
-          python-version: 3.6
+          python-version: 3.8
       - name: Install dependencies
         run: python -m pip install tox
       - name: Lint with tox