Iterate over expectedFeatures correctly

This fails if Array.prototype is extended.

Author: joshduck

src/browser/ui/React.js

@@ -130,7 +130,7 @@ if (__DEV__) {
       Object.freeze
     ];
 
-    for (var i in expectedFeatures) {
+    for (var i = 0; i < expectedFeatures.length; i++) {
       if (!expectedFeatures[i]) {
         console.error(
           'One or more ES5 shim/shams expected by React are not available: ' +