downgrade node to fix build issue

atom/node-keytar#386 (comment)

Author: PalmerAL

.github/workflows/build-packages.yml

@@ -9,7 +9,7 @@ jobs:
     - uses: actions/checkout@v2
     - uses: actions/setup-node@v2
       with:
-        node-version: '15.x'
+        node-version: '14.11.0'
     - run: npm install
     - name: build package
       run: npm run buildMacIntel && npm run buildMacArm