Stop using EOL Node in CI. (#11)

Author: felixfontein

.github/workflows/build-css.yml

@@ -21,7 +21,7 @@ jobs:
       - name: Use Node.js
         uses: actions/setup-node@v1
         with:
-          node-version: 12.x
+          node-version: 16.x
 
       - name: Install dependencies
         run: |