Fix Android Modal status bar translucency bug

This fixes the longstanding issue highlighted at this issue: facebook#7474

A janky postinstall fix making this exact change is quite popular on NPM, demonstrating that there's a clear need for this (see https://www.npmjs.com/package/react-native-modal-translucent)

Libraries/Modal/Modal.js

@@ -20,7 +20,7 @@ const PropTypes = require('prop-types');
 const StyleSheet = require('StyleSheet');
 const View = require('View');
 
-const RCTModalHostView = require('RCTModalHostViewNativeComponent');
+const RCTModalHostView = Platform.OS === 'ios' ? requireNativeComponent('RCTModalHostView') : requireNativeComponent('TranslucentModalHostView');
 
 const ModalEventEmitter =
   Platform.OS === 'ios' && NativeModules.ModalManager