Upgrade node because old npm is broken

.github/workflows/build.yaml

@@ -11,8 +11,9 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v2
         with:
-          node-version: '14'
-      - run: npm install
+          node-version: '15'
+
+      - run: npm ci
 
       - name: Typecheck
         run: npm run typecheck