Update ReactDOM for react v16 compatibility
Update ReactDOM for react v16 compatibility

It appears as is ReactDOM has been removed as of react v16. As a result, react-a11y throws the error "react-a11y: missing argument 'ReactDOM'". Updating the option check to look for `findDOMNode` instead.
reactjs/react-a11y,rackt/react-a11y,rackt/react-a11y