Update Node.js versions to 18 and 20 in CI and package.json

Co-authored-by: hsluoyz <3787410+hsluoyz@users.noreply.github.com>

Author: Copilot

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [ ^14, ^16, ^18 ]
+        node: [ ^18, ^20 ]
     steps:
       - uses: actions/checkout@v2
 

package.json

@@ -6,6 +6,9 @@
   "repository": "https://github.com/casbin/casbin.js.git",
   "author": "kingiw <kingiw@hotmail.com>",
   "license": "Apache-2.0",
+  "engines": {
+    "node": ">=18.0.0"
+  },
   "scripts": {
     "format": "prettier --write 'src/**/*.ts'",
     "lint": "yarn eslint . --ext .js,.jsx,.ts,.tsx --fix",