title: How can i set a default screen in using createStackNavigator combined with create createDrawerNavigator
body: <p>Im setting the routes of my react-native app and im trying to combine createStackNavigator and createDrawerNavigator. So, one of the screens in my drawer is a stackNavigator (ex: Home, News, Images. where Images is a stackNavigator) and the stackNavigator have two other screens (ex: Feed and Grid) and im trying to set the Feed as the default screen, so i always get redirected to the Feed.</p>
  
  <p>Ive tried something like: initialRouteName: 'Feed'</p>
  
  <p>But if navigate to the Grid than navigate to some screen in the Drawer then comeback to the "Images" it opens the Grid and not the Feed</p>
  
  <pre><code>const ImagesTab = createStackNavigator(
      {
          Feed: { screen: Feed },
          Grid: { screen: Grid },
      },
      {
          headerMode: 'none',
          navigationOptions: {
              headerVisible: false,
          }
      }
  )
  
  const AppDrawer = createDrawerNavigator({
  
      home: { screen: Home },
      news: { screen: News },
      images: { screen: ImagesTab },
      galeria: { screen: AppTabNavigator },
  },
      {
          contentComponent: DrawerContent
      }
  );
  </code></pre>