Force worfklow to run under node 12

.github/workflows/javascript-packages.yaml

@@ -16,10 +16,12 @@ jobs:
           # Make sure the actual branch is checked out when running on pull requests
             ref: ${{ github.head_ref }}
 
-        - name: Install dependencies
-          run: |
-            cd build/javascript
-            npm run build
+        - name: Build dependencies
+        - uses: actions/setup-node@v2
+          with:
+            node-version: '12'
+        - run: cd build/javascript
+        - run: npm run build
 
         - name: Commit changes
           uses: EndBug/add-and-commit@v5