run unit tests on Windows and macOS (#4908)

.github/workflows/ci.yml

@@ -24,7 +24,10 @@ jobs:
     - uses: actions/setup-node@v1
     - run: 'npm i && npm run lint'
   Unit:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macOS-latest]
     steps:
     - uses: actions/checkout@v1
     - uses: actions/setup-node@v1