Update markdownlint to new nde version

Author: adrain-cb

.github/workflows/hygeine.yml

@@ -48,7 +48,7 @@ jobs:
     - name: Set up Node.js
       uses: actions/setup-node@v2
       with:
-        node-version: '14' 
+        node-version: '15'
 
     - name: Install markdownlint CLI
       run: npm install -g markdownlint-cli