Propagate prop type flow through StyleContext.createContainer

Reviewed By: blairvanderhoof

Differential Revision: D4394074

fbshipit-source-id: f9c7f71ba921d345e3313a3a2be16a7f85a2e0af

Libraries/Image/ImageSource.js

@@ -12,5 +12,5 @@
 'use strict';
 
 export type ImageSource = {
-  uri: string,
+  uri?: string,
 } | number;