Summary:
The empty object literal `{}` now has the type `{}` - i.e. an exact empty object - rather than being unsealed.

Enable the option in the github flowconfigs

Changelog: [Internal]

Reviewed By: pieterv

Differential Revision: D37836634

fbshipit-source-id: 8ef0cfaf1d0420ae71723e04163f00c43c550e07