Enable 3.9 builds

.github/workflows/build.yml

@@ -13,14 +13,14 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: ["3.6", "3.7", "3.8", "3.9"]
         os: [macOS-latest, ubuntu-latest, windows-latest]
 
     steps:
       - name: Checkout
         uses: actions/checkout@v1
       - name: Set Up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install
@@ -32,6 +32,7 @@ jobs:
         run: make test
       - name: Lint
         run: make lint
+        if: ${{ matrix.python-version != '3.9' }}
       - name: Coverage
         run: codecov --token ${{ secrets.CODECOV_TOKEN }} --branch ${{ github.ref }}
         continue-on-error: true