message: package.json: add root lerna diff command
diff: "bundle": "yarn build && yarn workspace example-app bundle",
  "build": "lerna run build",
  "clean": "lerna run clean",
  + "diff": "lerna run diff --",
  "test": "yarn build && lerna run test --since origin/master -- --coverage",
  "test:all": "yarn build && lerna run test -- --coverage",
  "lint": "lerna run lint --since origin/master --",
  