Fix object equality check
Fix object equality check

The check ```statesAreEqual(a,b)``` currently returns ```true``` for ```a={x: 1}``` and ```b={x: 1, y: 2}```.
ReactJSTraining/history,mjackson/history,reactjs/history,reactjs/history,rackt/history,ReactTraining/history,mjackson/history,rackt/history,ReactJSTraining/history