title: setRootController error using react-native-navigation in Expo
body: <p>I keep running into <code>undefined is not an object (evaluating 'RCCManager.setRootController')</code> when trying to use react-native-navigation.</p>
  
  <p>I tried to follow suit with <a href="https://github.com/junedomingo/movieapp" rel="nofollow noreferrer">https://github.com/junedomingo/movieapp</a> but hit this when it tries to load the project in the Expo app.</p>
  
  <p>I've modified my App.js generated by Expo to look like this:</p>
  
  <pre class="lang-js prettyprint-override"><code>import HomeScreen from './screens/HomeScreen'
  
  Navigation.registerComponent('screens.HomeScreen', () =&gt; HomeScreen)
  
  class App extends React.Component {
    constructor(props) {
      super(props)
      this.startApp()
    }
    startApp() {
      Navigation.startTabBasedApp({
        tabs: [
          {
          label: 'One',
          screen: 'screens.HomeScreen',
          title: 'Screen One'
          },
        ]
      })
    }
  }
  
  const app = new App()
  </code></pre>
  
  <p>That's a bit boiled down, but I think those are the essential bits.  I feel like I'm not handing things off from rnn to Expo the way Expo is expecting.</p>
  
  <p>Any idea how to get rnn running in Expo?  If there's an example repo I can play with, that would be great.  I'm sure I can get rnn working outside Expo, so vanilla rnn examples probably won't help much.</p>