ZooKeeper release 3.5.6 document is not available on website

[Mohammad arshad]

Hello folks
ZooKeeper release 3.5.6 document 
http://zookeeper.apache.org/doc/r3.5.6/index.html is not available.
Does anyone have any idea why it is not available. Is it removed intentionally 
or it got removed by mistake.

Thanks
-Arshad