use py3.8

Author: ladyada

.github/workflows/githubci.yml

@@ -9,7 +9,7 @@ jobs:
     steps:
     - uses: actions/setup-python@v1
       with:
-        python-version: '3.x'
+        python-version: '3.8'
     - uses: actions/checkout@v2
     - uses: actions/checkout@v2
       with: