update gh actions (#156)

.github/workflows/npm-ci.yml

@@ -6,10 +6,10 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-node@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
         with:
-          node-version: 18.x
+          node-version: 20
       - run: npm ci
       - run: npm run jslint
       - run: npm test