Fix prop declaration
Fix prop declaration

Summary:
There's a mismatch as we don't use the same existential qualification
in the constructor as we do for the class definition. This this
enforced more strictly in newer Flow versions.

Reviewed By: danielbuechele

Differential Revision: D15601548

fbshipit-source-id: 807ef9ba74933fbc653514a617d1008f4f65c631

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper