title: tabBarIcon not displayed on createBottomTabNavigator
body: <p>Since I updated react-navigation (from v2 to v3), the icons I had in my createBottomTabNavigator no longer appear above the labels. When I look at the documentation I can not find the solution. Can you help me please ?</p>
  
  <p>The code of my bottom navigation :</p>
  
  <pre><code>import React from 'react';
  import {
      createAppContainer,
      createBottomTabNavigator,
      createStackNavigator,
      createSwitchNavigator
  } from 'react-navigation';
  import PronosticsScreen from "../screens/PronosticsScreen";
  import BookmakersScreen from "../screens/BookmakersScreen";
  import StatsScreen from "../screens/StatsScreen";
  import TabBarIcon from '../components/TabBarIcon';
  import {Platform} from "react-native";
  
  const PronosticsStack = createStackNavigator({
      Pronostics: PronosticsScreen,
  });
  
  PronosticsStack.navigationOptions = {
      tabBarLabel: 'Pronostics',
      tabBarIcon: ({focused}) =&gt; (
          &lt;TabBarIcon
              focused={focused}
              name={
                  Platform.OS === 'ios'
                      ? `ios-paper${focused ? '' : '-outline'}`
                      : 'md-paper'
              }
          /&gt;
      ),
  };
  
  const BookmakersStack = createStackNavigator({
      Bookmakers: BookmakersScreen,
  });
  
  BookmakersStack.navigationOptions = {
      tabBarLabel: 'Bookmakers',
      tabBarIcon: ({focused}) =&gt; (
          &lt;TabBarIcon
              focused={focused}
              name={
                  Platform.OS === 'ios'
                      ? `ios-paper${focused ? '' : '-outline'}`
                      : 'md-paper'
              }
          /&gt;
      ),
  };
  
  const StatsStack = createStackNavigator({
      Stats: StatsScreen,
  });
  
  StatsStack.navigationOptions = {
      tabBarLabel: 'Stats',
      tabBarIcon: ({focused}) =&gt; (
          &lt;TabBarIcon
              focused={focused}
              name={
                  Platform.OS === 'ios'
                      ? `ios-paper${focused ? '' : '-outline'}`
                      : 'md-paper'
              }
          /&gt;
      ),
  };
  
  const BottomTabNavigator = createBottomTabNavigator({
          Pronostics: PronosticsScreen,
          Bookmakers: BookmakersScreen,
          Stats: StatsScreen,
      },
      {
          tabBarOptions: {
              showIcon: true,
              activeTintColor: '#c7943e',
              activeBackgroundColor: '#000000',
              inactiveTintColor: '#c7943e',
              inactiveBackgroundColor: '#000000',
          },
      });
  
  const SwitchNavigator = createSwitchNavigator(
      {
          Bottom: BottomTabNavigator,
      }
  );
  
  export default createAppContainer(SwitchNavigator);
  </code></pre>
  
  <p>Moreover, my IDE tells me that the tabBarIcon property is not used..</p>
  
  <p><a href="https://i.stack.imgur.com/EUzpu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EUzpu.png" alt="enter image description here"></a></p>
  
  <p>Thank you in advance for your help</p>