Lock doesn't show up when String's prototype is modified

[gnandretta]

The following message is shown in the console (of the development build):

Uncaught Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. Check the render method of ReactTransitionGroup.

To reproduce add a new property to String.prototype in the page that includes Lock:

 String.prototype.hello = function() {
   return "hi!";
 }