Changed syntax to avoid browser warning.

Using the constructor for instantiating JSX components has been
deprecated:

https://gist.github.com/sebmarkbage/ae327f2eda03bf165261

Author: justin808

docs/api/mixins/State.md

@@ -72,6 +72,9 @@ var Tab = React.createClass({
     var isActive = this.isActive(this.props.to, this.props.params, this.props.query);
     var className = isActive ? 'active' : '';
     var link = Link(this.props);
+    var link = (
+      <Link {...this.props} />
+    );
     return <li className={className}>{link}</li>;
   }