title: uglifyjs drop_console / pure_funcs is not working in webpack
body: <p>I have the following configuration, but it still does not remove <code>console.log</code> statements:</p>
  
  <pre><code>new webpack.optimize.UglifyJsPlugin({
      compress: {
          warnings: false,
          pure_funcs: ['console.log'],
          drop_console: true,
          comments: false
      },
      pure_funcs: ['console.log'],
      drop_console: true,
      comments: false
  })
  </code></pre>
  
  <p>What am I doing wrong?</p>