[ci] Run tests on all supported node versions

.github/workflows/action.yml

@@ -1,13 +1,16 @@
 on: push
 name: Main Workflow
 jobs:
-  runNpmStuff:
+  tests:
+    strategy:
+      matrix:
+        node: ['16', '14', '12']
     name: Run NPM Stuff
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v1
     - uses: actions/setup-node@v2
       with:
-        node-version: '16'
+        node-version: ${{matrix.node}}
     - run: npm install
     - run: npm test