run tests on Windows and macOS

.github/workflows/ci.yml

@@ -8,12 +8,26 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    if: "!contains(github.event.head_commit.message, '[skip ci]')"
+    strategy:
+      matrix:
+        os:
+        - ubuntu-latest
+        - macos-latest
+        - windows-latest
+        node:
+        - 16
+        - 14
+        - 12
+      fail-fast: false
+    runs-on: ${{ matrix.os }}
+    name: Node ${{ matrix.node }} on ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-node@v2
       with:
-        node-version: '14.x'
+        node-version: ${{ matrix.node }}
     - run: yarn install --frozen-lockfile
+    - run: yarn audit
     - run: yarn lint
     - run: yarn test