title: extract-text-webpack-plugin not extracting css
body: <p>When I created chunk with the help of CommonChunkPlugin, extract-text-webpack-plugin doesn`t extract css from landings chunk. Any ideas?</p>
  
  <pre><code>config: {
  plugins: [
      new webpack.optimize.CommonsChunkPlugin({
          chunks: [
              'vzr',
              'vzrProduct',
              'emptyProduct'
          ],
          async: 'landings'
      }),
      new ExtractTextPlugin({
          filename: '[name].[contenthash].css',
          allChunks: true
      })
    ]
  }
  </code></pre>