add MacOS builds to GitHub actions (#193)

Author: bashbaug

.github/workflows/build.yml

@@ -30,7 +30,7 @@ jobs:
 
     strategy:
       matrix:
-        os: [ubuntu-latest, windows-latest]
+        os: [ubuntu-latest, windows-latest, macos-latest]
 
     runs-on: ${{matrix.os}}