Update ci.yml

Author: jpdakran

.github/workflows/ci.yml

@@ -10,10 +10,11 @@ on:
 
 jobs:
   main:
+    runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        python: ['3.6', '3.7', '3.8', '3.9']
-    runs-on: ubuntu-latest
+        os: [ubuntu-latest, macos-latest]
+        python: ['3.6', '3.7']
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-python@v2