DOMNode.setAttribute() expects the second param to be string
DOMNode.setAttribute() expects the second param to be string

This is only the half story, as other values are supported, but these
values would be coerce to string. So setting a string doesn't hurt us.

Fix #75
Fix #76

reactjs/react-tabs,mzabriskie/react-tabs,neeharv/react-tabs,rackt/react-tabs,reactjs/react-tabs