$ webpack

module.js:487

    throw err;

    ^

Error: Cannot find module 'webpack-sources'

    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> (E:\前端\mmall-fe\node_modules\extract-text-webpack-pl5:20)

    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)

不知道哪里错了