update node to 16 for CI

Author: bluebill1049

.github/workflows/main.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [12.x]
+        node-version: [16.x]
     steps:
       - uses: actions/checkout@v2
       - name: Use Node.js ${{ matrix.node-version }}