title: React-navigation: "You should only render one navigator" - but I have only one
body: <p>I just upgraded react-navigation to v2.0-rc9, and it complains that </p>
  
  <blockquote>
    <p>You should only render one navigator explicitly in your app, and other navigators should by rendered by including them in that navigator.</p>
  </blockquote>
  
  <p>I have only one navigator, as shown below, and I can't understand where that comes from. Could you please point to a possible cause for that error ? Below are my root component and the way I create the navigator.</p>
  
  <p>Root.js:</p>
  
  <pre><code>import React, { PureComponent } from 'react';
  import { Provider } from 'react-redux';
  import store from './store';
  import AppNavigation from './AppNavigation';
  
  class Root extends PureComponent {
      render() {
          return (
              &lt;Provider store={store}&gt;
                   &lt;AppNavigation/&gt;
              &lt;/Provider&gt;
          );
      }
  }
  
  export default Root;
  </code></pre>
  
  <p>AppNavigation.js:</p>
  
  <pre><code>import { createStackNavigator } from 'react-navigation';
  
  const AppNavigation = createStackNavigator({
      home: HomePage
  });
  
  export default AppNavigation;
  </code></pre>