Please provide enough information so that others can review your pull request:

## Motivation

Explain the **motivation** for making this change. What existing problem does the pull request solve?

## Test plan

Demonstrate the code is solid. Example: the exact commands you ran and their output, screenshots / videos if the pull request changes UI.

Make sure you test on both platforms if your change affects both platforms.

The code must pass tests.

## Code formatting

Look around. Match the style of the rest of the codebase. Run `yarn format` before committing.

## Changelog

Add an entry under the "Unreleased" heading in [CHANGELOG.md](https://github.com/react-navigation/react-navigation/blob/master/CHANGELOG.md#unreleased) which explains your change.
