update workflow

Author: kotarella1110

.github/workflows/main.yml

@@ -3,6 +3,9 @@ on: [push]
 jobs:
   build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [12.x]
     steps:
       - uses: actions/checkout@v2
       - name: Use Node.js ${{ matrix.node-version }}