Android backbutton mimimize with type:'reset'

### Version
- react-native-router-flux v4.0.6
- react v16.12.0
- react-native v0.61.4

### Expected behaviour
On type 'reset: When i press the android back button; if there is none pop action, it minimizes the app.
On type 'push' or default: When i press the android back button; if there is none pop action, it minimizes the app.

### Actual behaviour
On type 'reset: When i press the android back button; if there is none pop action, it doesn't do anything.

On type 'push' or default: When i press the android back button; if there is none pop action, it minimize the app.