Summary:
It seems like the `resizeMode` propType was missing from `Image.android.js`, this PR adds it.
I caught by trying to use `Image.propTypes.resizeMode` on Android, and getting a warning because it was `undefined`.
It's not supposed to break anything, maybe pop a few warnings but not much more.
**Test Plan:**
- Launched UIExplorer
Closes https://github.com/facebook/react-native/pull/7355
Differential Revision: D3648559
fbshipit-source-id: a4397938d14c11ded909d6bf4652a4b0fcebed3b
f634a0fc23