title: webpack-dev-server Cannot find module 'webpack'
body: <p>I'm trying to use webpack-dev-server to run a simple program
  but I'm getting this error:</p>
  
  <pre><code>module.js:471
      throw err;
      ^
  
  Error: Cannot find module 'webpack'
      at Function.Module._resolveFilename (module.js:469:15)
      at Function.Module._load (module.js:417:25)
      at Module.require (module.js:497:17)
      at require (internal/module.js:20:19)
      at Object.&lt;anonymous&gt; 
      at Module._compile (module.js:570:32)
      at Object.Module._extensions..js (module.js:579:10)
      at Module.load (module.js:487:32)
      at tryModuleLoad (module.js:446:12)
      at Function.Module._load (module.js:438:3)
  </code></pre>
  
  <p>I have installed webpack with following npm command</p>
  
  <pre><code>npm install --save-dev webpack
  </code></pre>
  
  <p>and I have the following configuration:</p>
  
  <pre><code>(webpack.config.js)
  var webpack = require('webpack');
  var path = require('path');
  
  var BUILD_DIR = path.resolve(__dirname, 'client/public');
  var APP_DIR = path.resolve(__dirname, 'client/app');
  
  var config = {
    entery: APP_DIR + '/index.js',
    output: {
      path: BUILD_DIR,
      filename: 'bundle,js',
    },
    module: {
      loaders: [
        {
          test: /.jsx?$/,
          loader: 'babel-loader',
          exclude: /node_modules/,
          query: {
            presets: ['es2015', 'react']
          }
        }
      ]
    }
  };
  
  module.exports = config;
  </code></pre>
  
  <p>I have tried everything and I'm really lost.
  Does anyone have any idea?</p>