title: React Navigation TabBarIcon not appearing
body: <p>I can't get a <code>TabBarIcon</code> to appear in my <code>TabNavigator.</code> I've read a bunch of posts from people with a similar issue, but their solutions don't work for me. I'd really just like to be able to have a PNG image component for each <code>TabBarIcon</code> but it just won't appear.</p>
  
  <pre><code>const Tabs = TabNavigator({
      Feed: {
        screen: FeedPage,
        navigationOptions: {
          tabBarLabel:"Feed",
          tabBarIcon: () =&gt; (&lt;Image source={require('./Resources/Images/TabBar Icons_Feed.png')} style={{height: 10, width: 10}} /&gt;)
        }
      },
      Me: {
        screen: MePage,
        navigationOptions: {
          tabBarLabel:"Me",
        }
      },
    },
    {
      initialRouteName: 'Me',
      tabBarOptions: {
        showIcon: true,
        showLabel: true
      }
    }
  );
  
  const RootStack = StackNavigator(
    {
      //All Tabs
      Tabs: {
        screen: Tabs,
      },
      //Other Pages
      Signup: {
        screen: SignupPage,
      },
      ProfilePicUploader: {
        screen: ProfilePicUploaderPage,
      },
      Login: {
        screen: LoginPage,
      },
      User: {
        screen: UserPage,
      },
      EasterEgg: {
        screen: EasterEggPage,
      },
    },
    {
      initialRouteName: 'Tabs',
      headerMode: 'none'
    }
  );
  
  export default class App extends Component&lt;Props&gt; {
    render() {
      return (
        &lt;RootStack/&gt;
      );
    }
  }
  </code></pre>
  
  <p>Anyone know what's going on?</p>