change github actions python version to 3.8

.github/workflows/publish-to-pypi.yml

@@ -11,10 +11,10 @@ jobs:
     - uses: actions/checkout@master
       with:
         fetch-depth: 10
-    - name: Set up Python 3.7
+    - name: Set up Python 3.8
       uses: actions/setup-python@v1
       with:
-        python-version: 3.7
+        python-version: 3.8
     - name: Install pypa/build
       run: |
         python3 -m pip install wheel