ci: use node 14 for build (#30)

Author: zepatrik

.github/workflows/build.yml

@@ -8,6 +8,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2-beta
+        with:
+          node-version: '14'
       - run: npm ci
       - name: Build bundles
         run: npm run build