update pypi.yml

.github/workflows/pypi.yml

@@ -6,11 +6,11 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        python-version: ['3.8']
     steps:
       - uses: actions/checkout@v2
+      - uses: actions/setup-python@v1
+        with:
+          python-version: '3.x'
       - name: Build dists
         run: |
           python3 setup.py sdist