add npm script to git clean except node_modules

package.json

@@ -16,7 +16,8 @@
     "localtunnel": "lt --port 3000",
     "share": "npm-run-all --parallel open:src localtunnel",
     "test": "mocha --reporter progress \"src/**/*.test.js\"",
-    "test:watch": "npm run test -- --watch"
+    "test:watch": "npm run test -- --watch",
+    "clean": "git clean -fdx -e node_modules"
   },
   "author": "JOJO",
   "license": "MIT",