Fix erroneous PropTypes access warning

src/umd/ReactUMDEntry.js

@@ -14,11 +14,11 @@
 var React = require('React');
 
 // `version` will be added here by the React module.
-var ReactUMDEntry = Object.assign({
+var ReactUMDEntry = Object.assign(React, {
   __SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED: {
     ReactCurrentOwner: require('ReactCurrentOwner'),
   },
-}, React);
+});
 
 if (__DEV__) {
   Object.assign(