Summary:
`responseType` should be a string, not an Object (which gets converted to a NativeMap by TM).
Changelog: [General] [Fixed] Fix the flow type for NativeNetworkingModule
Reviewed By: fkgozali
Differential Revision: D18019418
fbshipit-source-id: 316470ca82241223eafb5b05a54fc2bbf3074821