run github actions on all platforms

Author: Patrick Jackson

.github/workflows/test.yml

@@ -8,7 +8,10 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [macos-latest, windows-latest, ubuntu-latest]
     steps:
       - uses: actions/checkout@v2