Update build.yml

Author: youngbupark

.github/workflows/build.yml

@@ -16,7 +16,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     env:
-      NODE_VER: 12
+      NODE_VER: 12.18.2
     steps:
     - uses: actions/checkout@v2
     - name: Use Node.js