報錯：
ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! metools@1.0.0 dev: `node build/dev-server.js`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the metools@1.0.0 dev script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
---------------------
這個是報 的錯誤，原因是 webpack 的新版本的BUG，解決方法：
先卸載 npm remove webpack-dev-server
再安裝老版本 npm install webpack-dev-server@2.9.1
最后運行 npm run dev