Run npm test on all operating systems

.github/workflows/pr-checks.yml

@@ -65,9 +65,12 @@ jobs:
         echo "Success: node_modules are up to date"
 
   npm-test:
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-latest,macos-latest]
+    runs-on: ${{ matrix.os }}
 
     steps:
     - uses: actions/checkout@v1
     - name: npm run-script test
-      run: npm run-script test
+      run: npm run-script test