Summary:**Motivation**
AppStateIOS never currently returns `inactive` as a possible state. I had a requirement that when inactive, certain portions of the app should be blacked out in accordance with compliance rules. This is not possible currently, due to `inactive` never being returned. This PR fixes that.
**Test plan**
All base tests are passing. Are there AppState specific tests in place at the moment that I'm missing?
**Demonstration**
![appstate](https://cloud.githubusercontent.com/assets/286616/13640546/1cb6eeb0-e5e3-11e5-8d64-332ea3383a54.gif)
Closes https://github.com/facebook/react-native/pull/6379
Differential Revision: D3035530
Pulled By: nicklockwood
fb-gh-sync-id: 93deccc8184816809926dca8a95f2bebd1434987
shipit-source-id: 93deccc8184816809926dca8a95f2bebd1434987