Summary:
The appearance module uses sync native module methods which doesn't work with the chrome debugger. This broke in 0.62: https://github.com/facebook/react-native/issues/26705

This fix makes the appearance module return 'light' when using the chrome debugger.

Changelog: [Fixed] Appearance `getColorScheme` no longer breaks the debugger

Reviewed By: yungsters

Differential Revision: D20879779

fbshipit-source-id: ad49c66226096433bc9f270e004ad4a6f54fa8c2