specify node version to 12.18.2

Author: yeonjuan

.github/workflows/main.yml

@@ -10,7 +10,7 @@ jobs:
       - name: Use Node.js
         uses: actions/setup-node@v1
         with:
-          node-version: '12.x'
+          node-version: '12.18.2'
       - name: Install
         run: npm install
       - name: Build Lint