When user swipes back the keyboard is not hidden as user starts the swipe gesture

### Version
Tell us which versions you are using:

- react-native-router-flux v4.2.0
- react v16.11.0
- react-native v0.63.2

### Expected behaviour

When user swipes back from a screen where a TextInput is currently focused (and keyboard is shown) the keyboard should hide as user starts to swipe. It user cancels the swipe the keyboard should appear back.

I believe that KeyboardAwareNavigator that is used underneath should actually blur the TextInput that is currently focused. I see the console.error saying "currentlyFocusedField is deprecated and will be removed in a future release. Use currentlyFocusedInput", but I cannot figure out where does it come from (I wanted to insert `Keyboard.dismiss()` statement there).

### Actual behaviour

The keyboard is not being dismissed when user starts to swipe. Instead, the keyboard keeps being shown on the screen until user finishes swipe gesture and gets to previous screen.

### Steps to reproduce

Create a Stack with 2 scenes. In the second scene create a `` and try to swipe back from that scene.

### Reproducible Demo

I will try to create a demo today and paste the code here.