Added <Link scroll> PropType (#3003)

This should avoid the angry console warnings when trying to override the default scroll behavior using `<Link scroll={false}>`

lib/link.js

@@ -21,6 +21,7 @@ export default class Link extends Component {
     replace: PropTypes.bool,
     shallow: PropTypes.bool,
     passHref: PropTypes.bool,
+    scroll: PropTypes.bool,
     children: PropTypes.oneOfType([
       PropTypes.element,
       (props, propName) => {