title: fetch and Headers are undefined in IE11.0.9600 with babel-polyfill when process.env.NODE_ENV=='production'
body: <p>When <code>process.env.NODE_ENV=='development'</code> - it is OK!</p>
  
  <p>But our production build failed in IE 11 (11.0.9600).
  All work fine in chrome 55.</p>
  
  <p>devDependencies:</p>
  
  <pre><code>...
  babel-core: "6.22.0",
  babel-eslint: "^7.0.0",
  babel-loader: "^6.2.5",
  babel-preset-env: "^1.5.2",
  babel-preset-es2015: "^6.16.0",
  babel-preset-es2016: "^6.22.0",
  babel-preset-es2017: "^6.16.0",
  babel-preset-react: "^6.16.0",
  babel-preset-stage-0: "^6.22.0"
  ...
  </code></pre>
  
  <p>dependencies:</p>
  
  <pre><code>...
  babel-polyfill: "^6.16.0"
  ...
  </code></pre>
  
  <p>.babelrc:</p>
  
  <pre><code>{
      "presets": [
          "react",
          ["env", {
               "useBuiltIns": true
          }],
          "stage-0"
      ]
  }
  </code></pre>
  
  <p>Try <code>"useBuiltIns": false</code>, es2016, es2015, es2017 presets. Nothing changes.</p>
  
  <p>index.js:</p>
  
  <pre><code>"use strict";
  import 'babel-polyfill'
  ...
  </code></pre>
  
  <p>webpack.config module.exports.entry:</p>
  
  <pre><code>vendor: ['babel-polyfill', 'immutable', 'react', 'react-dom', ...],
  ...
  bundle: [path.resolve(__dirname, srcPath + ""index.js)]
  </code></pre>
  
  <p>vendor is the first script in index.html.</p>
  
  <p>Typing _babelPolyfill in ie console return true.
  But Headers, fetch are undefined...</p>
  
  <p>Why <code>process.env.NODE_ENV=='production'</code> broke my app in IE11?
  How to fix my config?</p>