title: Uglify, Cannot read property 'reset' of undefined
body: <p>I used webpack2 to build my app, but when use uglify-js + uglifyjs-webpack-plugin.I have some problems:</p>
  
  <pre><code>ERROR in vendors.js from UglifyJs
  TypeError: Cannot read property 'reset' of undefined
  at F:\Github\Program\My-test\Webpack\www2\node_modules\_uglifyjs-webpack-plugin@0.4.3@uglifyjs-webpack-plugin\dist\index.js:99:22
  at F:\Github\Program\My-test\Webpack\www2\node_modules\_uglifyjs-webpack-plugin@0.4.3@uglifyjs-webpack-plugin\dist\index.js:231:9
  at Array.forEach (native)
  at Compilation.&lt;anonymous&gt; (F:\Github\Program\My-test\Webpack\www2\node_modules\_uglifyjs-webpack-plugin@0.4.3@uglifyjs-webpack-plugin\dist\index.js:54:19)
  at Compilation.applyPluginsAsyncSeries (F:\Github\Program\My-test\Webpack\www2\node_modules\_tapable@0.2.6@tapable\lib\Tapable.js:142:13)
  at self.applyPluginsAsync.err (F:\Github\Program\My-test\Webpack\www2\node_modules\_webpack@2.5.1@webpack\lib\Compilation.js:635:10)
  at Compilation.applyPluginsAsyncSeries (F:\Github\Program\My-test\Webpack\www2\node_modules\_tapable@0.2.6@tapable\lib\Tapable.js:131:46)
  at sealPart2 (F:\Github\Program\My-test\Webpack\www2\node_modules\_webpack@2.5.1@webpack\lib\Compilation.js:631:9)
  at Compilation.applyPluginsAsyncSeries (F:\Github\Program\My-test\Webpack\www2\node_modules\_tapable@0.2.6@tapable\lib\Tapable.js:131:46)
  at Compilation.seal (F:\Github\Program\My-test\Webpack\www2\node_modules\_webpack@2.5.1@webpack\lib\Compilation.js:579:8)
  at F:\Github\Program\My-test\Webpack\www2\node_modules\_webpack@2.5.1@webpack\lib\Compiler.js:493:16
  at F:\Github\Program\My-test\Webpack\www2\node_modules\_tapable@0.2.6@tapable\lib\Tapable.js:225:11
  at _addModuleChain (F:\Github\Program\My-test\Webpack\www2\node_modules\_webpack@2.5.1@webpack\lib\Compilation.js:481:11)
  at processModuleDependencies.err (F:\Github\Program\My-test\Webpack\www2\node_modules\_webpack@2.5.1@webpack\lib\Compilation.js:452:13)
  at _combinedTickCallback (internal/process/next_tick.js:73:7)
  at process._tickCallback (internal/process/next_tick.js:104:9)
  </code></pre>
  
  <p>The webpack config maybe give some help to you:</p>
  
  <pre><code>module.exports = {
      entry: {
          app: path.resolve(APP, 'index.js'),
          vendors: ['jquery', 'moment']
      },
      output: {
          path: BUILD,
          filename: 'bundle.js'
      },
      plugins: [
          new HTMLwebpackPlugin({
              title: 'Generate by webpack'
          }),
          new webpack.optimize.CommonsChunkPlugin({
              name: 'vendors',
              filename: 'vendors.js'
          }),
          new UglifyJSPlugin({
              compress: true
          })
      ],
      module: {
          loaders: [
              {
                  test: /\.scss$/,
                  loaders: 'style-loader!css-loader?sourceMap!sass-loader?sourceMap',
                  include: APP 
              },
              {
                  test: /\.(jpg|png)$/,
                  loaders: 'url-loader?limit=40000'
              },
              {
                  test: /\.jsx?$/, 
                  loader: 'babel-loader',
                  include: APP,
                  query: {
                      presets: ['es2015', {"modules": false}]
                  }
              }
          ]
      },
      devtool: 'eval-source-map'
  }
  </code></pre>
  
  <p>What's the 'reset' mean? I can't find answer in anywhere...
  Thanks!</p>