message: utils build add presets
diff: "bootstrap": "yarn || npm i",
  "dev": "npm run build:file && webpack-dev-server --inline --config build/webpack.config.dev.js --content-base ./",
  "build:file": "node build/bin/build-entry.js",
  - "build:utils": "cross-env BABEL_ENV=utils babel src --out-dir lib --ignore src/index.js",
  + "build:utils": "cross-env BABEL_ENV=utils babel src --out-dir lib --ignore src/index.js --presets=es2015",
  "build:components": "cross-env NODE_ENV=production webpack --progress --hide-modules --config build/webpack.components.js --color",
  "build:vant-css": "gulp build --gulpfile packages/vant-css/gulpfile.js --color && cp -R packages/vant-css/lib/ lib/vant-css",
  "build:vant": "cross-env NODE_ENV=production webpack --progress --hide-modules --color --config build/webpack.build.js && cross-env NODE_ENV=production webpack -p --progress --hide-modules --color --config build/webpack.build.js",
  