title: React-native: this.navigator.pop not working
body: <p>I am new to react-native. I used the react-native-navbar package to go back to the previous route <a href="https://github.com/react-native-fellowship/react-native-navbar" rel="nofollow">navbar component for react-native</a></p>
  
  <p>when I click on the navbar button it shows me an error "<code>undefined is not an object(evaluating 'this.navigator.pop')</code>"</p>
  
  <p>here is my snippet:</p>
  
  <pre><code>'use strict';
  var React = require('react-native');
  var {
      StyleSheet,
      Text,
      View,
  } = React;
  var NavigationBar = require('react-native-navbar');
  var Demo = React.createClass({
      render: function()
      {
          var leftButtonConfig = {
            title: 'Back',
            handler: function onNext() {
              this.navigator.pop();
            }
          };
  
          var titleConfig = {
            title: 'Hello world page!',
          };
          return(
              &lt;View style={{ flex: 1, }}&gt;
        &lt;NavigationBar
          title={titleConfig}
          leftButton={leftButtonConfig} /&gt;
  
              &lt;View style={styles.container}&gt;
          &lt;Text style={styles.header}&gt;
          Hello World
          &lt;/Text&gt;
          &lt;/View&gt;
          &lt;/View&gt;
          );
      }
  });
  var styles = StyleSheet.create({
      container: {
          flex:1
      },
      header: {
          fontSize: 20,
          fontWeight: 'bold',
          textAlign: 'center'
      }
  });
  
  module.exports = Demo;
  </code></pre>