title: Webpack doesn't run clean when watch is set to true
body: <p>This is my webpack.config.js file:</p>
  
  <pre><code>const path = require('path');
  const ExtractTextPlugin = require('extract-text-webpack-plugin');
  const HtmlWebpackPlugin = require('html-webpack-plugin');
  
  const config = {
      entry: {
          bundle: './javascript/index.js'
      },
      output: {
          path: path.resolve(__dirname, 'build'),
          filename: '[name].[chunkhash].js'
      },
      module: {
          rules: [
              {
                  use: 'babel-loader',
                  test: /\.js$/,
                  exclude: /node_modules/
              },
              {
                  test: /\.css$/,
                  use: ExtractTextPlugin.extract({
                      fallback: "style-loader",
                      use: "css-loader"
                  })
              },
              {
                  test: /\.(jpe?g|png|gif|svg)$/,
                  use: [
                      {
                          loader: 'url-loader',
                          options: {
                              limit: 40000
                          }
                      },
                      'image-webpack-loader'
                  ]
              }
          ]
      },
      plugins: [
          new ExtractTextPlugin('style.css'),
          new HtmlWebpackPlugin({
              template: 'src/index.html'
          })
      ],
      watch: true
  };
  
  module.exports = config;
  </code></pre>
  
  <p>As you can tell from the last line I'm setting the watch option to true. In addition, I'm using chunkhash to generates a new javascript file when I make a change to any of my javascript files. However, it is not running my rinraf clean command when the watch option is set to 'true'.</p>
  
  <p>Here is a portion of my package.json file that:</p>
  
  <pre><code>{
      "name": "budgety",
      "version": "1.0.0",
      "description": "Budget app",
      "main": "app.js",
      "scripts": {
        "clean": "rimraf build",
        "build": "npm run clean &amp;&amp; webpack"
      },
  .
  .
  .
  </code></pre>
  
  <p>Why is this happening?</p>
  
  <p>My goal is to:</p>
  
  <ol>
  <li><p>Have my compiled javascript be updated after I update any of my javascript files, so I don't need to run 'npm run build' every single time I make a change to my js files.</p></li>
  <li><p>Clean the old javascript 'hashed' file which used be taken care of by 'rimraf' but for some reason it isn't cleaning the new hashed javascript files in watch mode.</p></li>
  </ol>