React native router flux - adding router hides title

### Version
Tell us which versions you are using:
- react-native-router-flux v4.2.0
- react v16.9.0
- react-native v0.61.5

### Expected behaviour

The drawer icon should be added next to the title

### Actual behaviour

I have the following stack in my router index.js file:

When I add the `drawer` attribute (as above), I don't see any title in my nav bar (just the menu icon).