Update build.yml

Author: electronstudio

.github/workflows/build.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: macos-10.15
     strategy:
       matrix:
-        python-version: [  3.9 ]
+        python-version: [ 3.6, 3.7, 3.8, 3.9 ]
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
       - uses: actions/checkout@v2