fix props anchor links

Summary:All anchor links are broken because of https://github.com/facebook/react-native/blob/master/website/core/Site.js#L37 base tag it means that relative urls won't work.
closes #5450
proof
![screen shot 2016-02-29 at 13 34 35](https://cloud.githubusercontent.com/assets/1488195/13392082/3d14a00e-dee9-11e5-8611-bc6bfaf6c752.png)
Closes https://github.com/facebook/react-native/pull/6208

Differential Revision: D2988892

Pulled By: vjeux

fb-gh-sync-id: da8b621af92d792a258812e38ae15f7cf53873ca
shipit-source-id: da8b621af92d792a258812e38ae15f7cf53873ca