Add cleanup command to remove node_modules folder when done developing.

Author: bennadel

demos/ng-18-hello-world/package.json

@@ -2,6 +2,7 @@
   "name": "app",
   "version": "0.0.0",
   "scripts": {
+    "cleanup": "rm -rf ./node_modules/",
     "ng": "ng",
     "start": "ng serve",
     "build": "ng build",