Update publish action to use Python3

.github/workflows/pypipublish.yml

@@ -8,11 +8,9 @@ jobs:
   deploy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - name: Set up Python
-        uses: actions/setup-python@v1
-        with:
-          python-version: '2.7'
+        uses: actions/setup-python@v2
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip