Bump node environment to 15.x

It updates node version to 15.x to be able to use
`String.prototype.replaceAll()`

.github/workflows/quality-checks.yaml

@@ -20,7 +20,7 @@ jobs:
       - name: Setup node
         uses: actions/setup-node@v1
         with:
-          node-version: 14.x
+          node-version: 15.x
       - name: Install dependencies
         run: npm ci
       - name: Lint