Summary:
The new `ViewabilityConfig` API has a typo:
`itemVisiblePercentThreashold` should be `itemVisiblePercentThreshold`.
Thought it would be good to fix this before people start depending on a property containing a typo :-)
Updated tests to match.
Closes https://github.com/facebook/react-native/pull/12593
Differential Revision: D4619798
Pulled By: ericvicenti
fbshipit-source-id: 0aa8b6cf9ae7e5638607195759e4bd51140667fe
9217ff3203