message: add a clean command
diff: "typescript": "3.4.5"
  },
  "scripts": {
  + "clean": "git clean -x -f",
  "compile": "tsc",
  "prepare": "npm run compile",
  "test": "npm run lint:deps && npm run lint:js && npm run node-tests && npm run ember-tests && npm run truffle-tests",
  