title: FlatList is not rendering my data inside react-native-tab-view
body: <p>I have a state <code>this.state.mantras</code> which gets updated everytime I post a new <code>mantra</code>. </p>
  
  <p>I have a component with a FlatList to render each of the mantras. However, the FlatList is not rendering anything. I am able to console.log the state which logs the updated state of the mantras array every time.</p>
  
  <p>I have a feeling that it's caused by something to do with react-native-tab-view within which I am trying to render the flatlist. </p>
  
  <pre><code>SecondRoute = () =&gt; (
      &lt;FlatList
        keyExtractor={(item, index) =&gt; index.toString()}
        numColumns={1}
        data={this.state.mantras}
        renderItem={this._renderItem}
      /&gt;
  )
  
  render() {
   console.log(this.state) &lt;-- success
    return (
     &lt;TabView
      renderTabBar={props =&gt;
        &lt;TabBar
          bounces
          {...props}
          style={styles.tabStyle}
        /&gt;
      }
      navigationState={this.state}
      renderScene={SceneMap({
        second: this.SecondRoute, &lt;--- fails to render, no errors
      })}
      onIndexChange={index =&gt; this.setState({ index })}
      initialLayout={{ width: Dimensions.get('window').width }}
     /&gt;
    )
   }
  
  _renderItem = ({item, index}) =&gt; (
    &lt;View&gt;
     &lt;View style={styles.mantraCard} key={item.id}&gt;
     &lt;Text style={styles.title}&gt;{item.title}&lt;/Text&gt;
     &lt;Text style={styles.description}&gt;{item.description}&lt;/Text&gt;
     &lt;/View&gt;
    &lt;/View&gt;
  );
  </code></pre>