[ReactNative] Fix secure text entry

Summary:
@public

`validAttributes` strikes again.

Test Plan: secure box in example is actually secure

Libraries/ReactNative/createReactNativeComponentClass.js

@@ -35,6 +35,7 @@ var createReactNativeComponentClass = function(
     this.previousFlattenedStyle = null;
   };
   Constructor.displayName = viewConfig.uiViewClassName;
+  Constructor.viewConfig = viewConfig;
   Constructor.prototype = new ReactNativeBaseComponent(viewConfig);
   Constructor.prototype.constructor = Constructor;