Fix StyleSheet 'textAlign' for AndroidTextInput. Closes #2702

Summary:
change `setTextAlign` and `setTextAlignVertical` to receive argument of type `String` (the same as in `StyleSheet`), so that native props and stylesheet props are calling the same ReactMethod

- add demo (may not be necessary)
Closes https://github.com/facebook/react-native/pull/4481

Reviewed By: svcscm

Differential Revision: D2823456

Pulled By: mkonicek

fb-gh-sync-id: 349d17549f419b5bdc001d70b583423ade06bfe8

Libraries/Text/TextStylePropTypes.js

@@ -46,6 +46,12 @@ var TextStylePropTypes = Object.assign(Object.create(ViewStylePropTypes), {
   textAlign: ReactPropTypes.oneOf(
     ['auto' /*default*/, 'left', 'right', 'center', 'justify']
   ),
+  /**
+   * @platform android
+   */
+  textAlignVertical: ReactPropTypes.oneOf(
+    ['auto' /*default*/, 'top', 'bottom', 'center']
+  ),
   /**
    * @platform ios
    */