title: Babel Error: Plugin/Preset files are not allowed to export objects, only functions
body: <p>I'm trying to run storybook on an expo installation. So I only got expo and storybook in the app so far.</p>
  
  <p>I'm not able to start the storybook for web.</p>
  
  <p>My package.json looks like this:</p>
  
  <pre><code>"dependencies": {
    "expo": "^32.0.0",
    "react": "16.5.0",
    "react-native": "https://github.com/expo/react-native/archive/sdk-32.0.0.tar.gz"
  },
  "devDependencies": {
    "@babel/core": "^7.2.2",
    "@babel/preset-env": "^7.2.3",
    "@babel/preset-react": "^7.0.0",
    "@babel/runtime": "^7.2.0",
    "@storybook/addon-actions": "^4.1.6",
    "@storybook/addon-knobs": "^4.1.6",
    "@storybook/addon-links": "^4.1.6",
    "@storybook/addon-ondevice-knobs": "^4.1.6",
    "@storybook/addon-ondevice-notes": "^4.1.6",
    "@storybook/addons": "^4.1.6",
    "@storybook/react": "^4.1.6",
    "@storybook/react-native": "^4.1.6",
    "babel-loader": "^7",
    "babel-preset-expo": "^5.0.0",
    "prop-types": "^15.6.2",
    "react-dom": "16.5.0"
  },
  </code></pre>
  
  <p>My babel.config.js looks like this;</p>
  
  <pre><code>module.exports = function(api) {
    api.cache(true);
    return {
      presets: ['babel-preset-expo'],
    };
  };
  </code></pre>
  
  <p>I have also tried with:</p>
  
  <pre><code>module.exports = function(api) {
    api.cache(true);
    return {
      presets: ["@babel/env", "@babel/react"],
    };
  };
  </code></pre>
  
  <p>I get this error when trying to run the storybook:</p>
  
  <pre><code>ERROR in ./storybook/addons.js
  Module build failed (from ./node_modules/@storybook/react-native/node_modules/babel-loader/lib/index.js):
  Error: Plugin/Preset files are not allowed to export objects, only functions. In /Users/kristoffernielsen/repos/app/storybook/node_modules/babel-preset-react/lib/index.js
      at createDescriptor (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-descriptors.js:178:11)
      at items.map (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-descriptors.js:109:50)
      at Array.map (&lt;anonymous&gt;)
      at createDescriptors (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-descriptors.js:109:29)
      at createPresetDescriptors (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-descriptors.js:101:10)
      at passPerPreset (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-descriptors.js:58:96)
      at cachedFunction (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/caching.js:33:19)
      at presets.presets (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-descriptors.js:29:84)
      at mergeChainOpts (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-chain.js:320:26)
      at /Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-chain.js:283:7
      at buildRootChain (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/config-chain.js:68:29)
      at loadPrivatePartialConfig (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/partial.js:85:55)
      at Object.loadPartialConfig (/Users/kristoffernielsen/repos/app/storybook/node_modules/@babel/core/lib/config/partial.js:110:18)
      at Object.&lt;anonymous&gt; (/Users/kristoffernielsen/repos/app/storybook/node_modules/@storybook/react-native/node_modules/babel-loader/lib/index.js:140:26)
      at Generator.next (&lt;anonymous&gt;)
      at asyncGeneratorStep (/Users/kristoffernielsen/repos/app/storybook/node_modules/@storybook/react-native/node_modules/babel-loader/lib/index.js:3:103)
   @ multi ./storybook/addons.js ./node_modules/@storybook/react-native/dist/manager/index.js manager[0]
  </code></pre>
  
  <p>It fails even though my addons.js is empty. </p>