fix: use older node for deploying

.github/workflows/firebase-merge.yml

@@ -8,6 +8,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
+      - name: Set up Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: 16
       - run: yarn install --frozen-lockfile && yarn build
       - run: |
           cd functions