title: Nest StackNavigator in a custom BottomTabNavigator, React Navigation V>2
body: <p>I have a project configured with <code>React Navigation</code> V1. when i update <code>React Navigation</code> to version 2, tab icons is disappears... this is the routing structure:</p>
  
  <pre><code>public static Routes = createStackNavigator({
      Splash: { screen: Splash },
      EditProfile: { screen: EditProfile },
      Main: {
          screen: createBottomTabNavigator({
              Search: {
                  screen: createStackNavigator({
                      Home: { screen: Home },
                      DoctorList: { screen: DoctorList },
                  }, stackConfig('Home')
                  )
              },
              Bookmark: {
                  screen: createStackNavigator({
                      BookmarkList: { screen: BookmarkList },
                  }, stackConfig('BookmarkList')
                  )
              },
              User: {
                  screen: createStackNavigator({
                      Profile: { screen: Profile },
                  }, stackConfig('Profile')
                  )
              },
          }, tabConfig('Search'))
      }
  }, stackConfig('Splash')
  )
  
  
  let stackConfig = (initialRouteName: any): any =&gt; {
      return {
          initialRouteName: initialRouteName,
          headerMode: 'none',
          cardStyle: {
              backgroundColor: 'transparent'
          },
      }
  }
  
  let tabConfig = (initialRouteName: any): any =&gt; {
      return {
          initialRouteName: initialRouteName,
          tabBarComponent: TabBarComponent,
          tabBarPosition: 'bottom',
          tabBarOptions: {
              labelStyle: {
                  fontFamily: Utility.font,
                  fontSize: Platform.OS !== 'ios' ? 9 : 11,
                  margin: 0,
              },
              activeTintColor: '#2e9699',
              inactiveTintColor: 'black',
              showIcon: true,
              showLabel: true,
              indicatorStyle: {
                  backgroundColor: 'red',
              },
              style: {
                  zIndex: 1,
                  backgroundColor: "#ffffff",
                  height: 60
              }
          }
      }
  }
  </code></pre>
  
  <p>output:</p>
  
  <p><a href="https://i.stack.imgur.com/EATSc.png" rel="noreferrer"><img src="https://i.stack.imgur.com/EATSc.png" alt="enter image description here"></a></p>
  
  <p>When i remove StackNavigator from a tab ( ex: <code>User: Profile</code> ), icon will appears correctly. i think a difference between V1 and V2 causes this but i don't know it.</p>
  
  <p>For example, <code>Profile.tsx</code> is like this:</p>
  
  <pre><code>export default class Profile extends Component {
      static navigationOptions = {
          tabBarIcon: ({ tintColor, focused }) =&gt; (
              &lt;Icon name="md-person" size={27} color={focused ? colors.green : colors.black} /&gt;
          )
      };
  }
  </code></pre>
  
  <p>Thanks.</p>