title: react-navigation undefined is not a function (evaluating '(0 _reactnavigation.StackNavigator)')
body: <p>I'm building a new project. Then I'm installing the react-navigation but it's not working.</p>
  
  <p><strong>Code</strong> :</p>
  
  <pre><code>import { StackNavigator, } from 'react-navigation';
  import Intro from './src/pages/Intro';
  
  const AppNavigator = StackNavigator({
    Intro: {
      screen: Intro,
      navigationOptions: {
        title: "Intro",
        header: null,
        navigationBar: null
      },
    },
  });
  export default class App extends Component {
    render() {
      return (
        &lt;AppNavigator /&gt;
      );
    }
  }
  </code></pre>
  
  <p><strong>Error</strong> : </p>
  
  <p><a href="https://i.stack.imgur.com/aKfg3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aKfg3.png" alt="enter image description here"></a></p>
  
  <p>========================================</p>