title: Can't get webpack-dev-server proxy and watch work together
body: <p>I'm trying to get work together webpack and PHP.</p>
  
  <p>The proxying to PHP built-in webserver works but it loses the ability to watch for changes on index.php and the rest of PHP files.
  Watching js files works correct.</p>
  
  <p>Package.json</p>
  
  <pre><code>"devDependencies": {
      "webpack": "^2.1.0-beta.21",
      "webpack-dev-server": "^1.15.0"
    },
  "scripts": {
      "backend": "cd src &amp;&amp; php -S localhost:9000",
      "server": "webpack-dev-server --inline --colors --progress --display-error-details --display-cached --port 3000 --content-base src",
      "start": "start npm run backend &amp;&amp; start npm run server"
    }
  </code></pre>
  
  <p>webpack.config.js</p>
  
  <pre><code>devServer: {
      proxy: {
          '/': {
              target: {
                  host: "localhost",
                  port: 9000,
                  protocol: "http"
              }
          }
      },
  },
  watch: true,
  </code></pre>
  
  <p>Without a proxy the watch and livereload work correct (on index.html file).</p>
  
  <p>How can I tell the webpack-dev-server to watch php files explicitly?</p>
  
  <p>Maybe the way I'm using for getting the PHP proxying is wrong or too complicated? I'd like to hear for other solutions.</p>
  
  <p>Thanks</p>