revert D2372548 to fix initial app state issue

Reviewed By: @hedgerwang

Differential Revision: D2480492

Libraries/AppStateIOS/AppStateIOS.ios.js

@@ -122,7 +122,11 @@ var AppStateIOS = {
     _eventHandlers[type].delete(handler);
   },
 
-  currentState: (RCTAppState && RCTAppState.initialAppState : ?string),
+  // TODO: getCurrentAppState callback seems to be called at a really late stage
+  // after app launch. Trying to get currentState when mounting App component
+  // will likely to have the initial value here.
+  // Initialize to 'active' instead of null.
+  currentState: ('active' : ?string),
 
 };