Summary:
Flow is moving the react-dom libdef to flow-typed. To prepare for that, we should add `react-dom_v16.x.x` to the react-native library definitions
Changelog: [Internal]
Reviewed By: samwgoldman
Differential Revision: D19726257
fbshipit-source-id: b2dcbc938b482b73947cc2683b87229873b573dd