Update ci.yml

Change deployments to use Python 3.

.github/workflows/ci.yml

@@ -79,10 +79,10 @@ jobs:
     if: github.event_name == 'push' && contains(github.ref, 'refs/tags/')
     steps:
       - uses: actions/checkout@v2
-      - name: Set up Python 2.7
+      - name: Set up Python 3.8
         uses: actions/setup-python@v2
         with:
-          python-version: 2.7
+          python-version: 3.8
       - name: Install pypa/build
         run: python -m pip install build
       - name: Build a binary wheel and a source tarball