Summary: Corrected computation of RCText element height with padding (padding was counted twice).
See also issue #2466.
Closes https://github.com/facebook/react-native/pull/2838
Reviewed By: @svcscm
Differential Revision: D2535924
Pulled By: @nicklockwood
fb-gh-sync-id: b9527803c0a5a6eed1db7e37c98b628750ab2045