包安装后，启动缺少 util

[herbomiy]

版本信息： vue：2.5.17 node：v8.11.3 npm: 5.6.0 错误信息： This dependency was not found:

• util in ./~/readable-stream/lib/_stream_readable.js, ./~/readable-stream/lib/internal/streams/BufferList.js

To install it, you can run: npm install --save util

Listening at http://localhost:8001