title: webpack-dev-server does not watch for my file changes
body: <p>When I change my files while webpack-dev-server is running, the bundle's files are not updated.
  Here are my webpack.config.js and package.json files, as you can see from my npm script, I've solved running <code>webpack watch</code> and <code>webpack-dev-server</code> in the same command (<code>npm run watch &amp;  webpack-dev-server --content-base ./ --port 9966</code>):</p>
  
  <p>webpack.config.js:</p>
  
  <pre><code>'use strict';
  
  var ReactStylePlugin = require('react-style-webpack-plugin');
  var ExtractTextPlugin = require('extract-text-webpack-plugin');
  
  var webpack = require('webpack');
  
  module.exports = {
      devtool: 'sourcemap',
    entry: ['./js/main.js'],
    output: {
      filename: 'bundle.js',
      path: __dirname + '/assets',
      publicPath: __dirname + '/'
    },
    module: {
      loaders: [
        {
          test: /\.js$/,
          loaders: [
            ReactStylePlugin.loader(),
            'jsx-loader?harmony'
          ]
        },
        {
          test: /\.css$/,
          loader: ExtractTextPlugin.extract('css-loader')
        }
      ]
    },
    plugins: [
      new ReactStylePlugin('bundle.css'),
      new webpack.DefinePlugin({
        'process.env': {
          // To enable production mode:
          //NODE_ENV: JSON.stringify('production')
        }
      })
    ]
  }
  </code></pre>
  
  <p>package.json:</p>
  
  <pre><code>{
    "name": "reactTest",
    "version": "1.0.0",
    "description": "",
    "main": "index.js",
    "scripts": {
      "test": "echo \"Error: no test specified\" &amp;&amp; exit 1",
      "watch": "webpack --watch",
      "build": "webpack",
      "web": "npm run watch &amp;  webpack-dev-server --content-base ./ --port 9966"
    },
    "author": "",
    "license": "ISC",
    "devDependencies": {
      "css-loader": "^0.10.1",
      "extract-text-webpack-plugin": "^0.3.8",
      "jsx-loader": "^0.13.1",
      "react-style-webpack-plugin": "^0.4.0",
      "style-loader": "^0.10.2",
      "url-loader": "^0.5.5",
      "webpack": "^1.8.5",
      "webpack-dev-server": "^1.8.0"
    },
    "dependencies": {
      "react": "^0.13.1",
      "react-style": "^0.5.3"
    }
  }
  </code></pre>
  
  <p>my directory structure is:</p>
  
  <pre><code>assets  
    bundle.css
    bundle.css.map    
    bundle.js 
    bundle.js.map 
  js
    AppActions.js
    Profile.css.js
    ProfileList.js
    main.js
    AppConstants.js
    AppStore.js       
    Profile.js
    ResultPage.js     
  package.json
  index.html
  node_modules
  webpack.config.js
  </code></pre>
  
  <p>every file inside <code>assets</code> directory is generated by webpack</p>