Run tests on Ubuntu 20.04 and MacOS

Author: flashcode

.github/workflows/ci.yml

@@ -6,12 +6,14 @@ jobs:
 
   build:
 
-    name: Python ${{ matrix.python-version }}
-    runs-on: ubuntu-latest
     strategy:
       matrix:
+        os: [ubuntu-20.04, macos-latest]
         python-version: [3.6, 3.7, 3.8]
 
+    name: Python ${{ matrix.python-version }} on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+
     steps:
 
       - uses: actions/checkout@v2