Correct typo on line 164

"Choices who're property" edited to "Choices whose property."

Before:
![screen shot 2014-11-11 at 11 09 16 am](https://cloud.githubusercontent.com/assets/3811225/4999065/62842610-6993-11e4-8c24-b1f93d981ee0.png)

After:
![screen shot 2014-11-11 at 11 09 47 am](https://cloud.githubusercontent.com/assets/3811225/4999068/6ae6ddfc-6993-11e4-8701-ef1240c84ae5.png)