Fix Select onChange prop
Fix Select onChange prop

Summary: Was passing in a Proxy instance before instead of a string. Now it passes the correct string that callers would expect.

Reviewed By: sjkirby

Differential Revision: D10181911

fbshipit-source-id: 8dfa677479a81de0f7b5be23f827ce7b52169931

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