Trial of changes to fix #31

#31 might be fixed by https://github.com/actions/checkout#Checkout-pull-request-HEAD-commit-instead-of-merge-commit - one way to find out!

.github/workflows/node.js.yml

@@ -23,3 +23,23 @@ jobs:
     - run: npm ci
     - run: npm run build --if-present
     - run: npm test
+
+  build-head-sha:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [12.x, 14.x]
+
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        ref: ${{ github.event.pull_request.head.sha }}
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - run: npm ci
+    - run: npm run build --if-present
+    - run: npm test