Update pr.yml

Need multiple version support

Author: thorough-developer

.github/workflows/pr.yml

@@ -10,11 +10,14 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node: [ '14', '13', '12']
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v1
         with:
-          node-version: 12
+          node-version: ${{ matrix.node }}
       - run: npm ci
       - run: npm test
       - run: npm run benchmark