title: react native navigator push undefined crash first route
body: <p>index.ios.js</p>
  
  <pre><code>render: function() {
      return (
          &lt;NavigatorIOS
              style={styles.navigationContainer}
              initialRoute={{
              title: "Stories",
              component: Stories,
              leftButtonTitle : 'blabla',
              rightButtonTitle : 'Profile',
              onLeftButtonPress: () =&gt; {
               // this.blabla()
              },
              onRightButtonPress: () =&gt; {
               this.goProfile();
              }
          }} /&gt;
      );
  }
  </code></pre>
  
  <p>goProfile function </p>
  
  <pre><code>goProfile : function  () {
       this.props.navigator.push({
            title: 'Profile',
            component: profilePage,
            leftButtonTitle: 'Home',
        });
  },
  </code></pre>
  
  <p>Cannot read property 'push' of undefined
  This object props have  only rootTag in object.
  Why crash on the first page application . </p>