webpack 4.X npm run start 报错

package.json:

{
  "name": "webpack",
  "version": "1.0.0",
  "description": "",
  "main": "webpack.config.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "build": "webpack",
    "start": "webpack-dev-server"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "jquery": "^3.3.1"
  },
  "devDependencies": {
    "webpack-dev-server": "^3.1.5"
  }
}

bogon:webpack cristin$ npm run start

> [email protected] start /Users/cristin/Documents/webpack
> webpack-dev-server

module.js:487
throw err;
^

Error: Cannot find module 'webpack'
at Function.Module._resolveFilename (module.js:485:15)
at Function.Module._load (module.js:437:25)
at Module.require (module.js:513:17)
at require (internal/module.js:11:18)
at Object.<anonymous> (/Users/cristin/Documents/webpack/node_modules/webpack-dev-server/lib/Server.js:22:17)
at Module._compile (module.js:569:30)
at Object.Module._extensions..js (module.js:580:10)
at Module.load (module.js:503:32)
at tryModuleLoad (module.js:466:12)
at Function.Module._load (module.js:458:3)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! [email protected] start: `webpack-dev-server`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the [email protected] start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! /Users/cristin/.npm/_logs/2018-07-23T03_08_57_715Z-debug.log
bogon:webpack cristin$ sudo npm install webpack-dev-server
Password:
npm WARN [email protected] requires a peer of webpack@^4.0.0-beta.1 but none is installed. You must install peer dependencies yourself.
npm WARN [email protected] requires a peer of webpack@^4.0.0 but none is installed. You must install peer dependencies yourself.
npm WARN [email protected] No description
npm WARN [email protected] No repository field.

+ [email protected]
updated 2 packages in 12.044s
bogon:webpack cristin$