A critical Zookeeper bug could affect helix

[tohidemyname]

Describe the bug and how to reproduce

The latest Helix calls zookeeper 3.6.3. Some bugs of this version can affect Helix. For example, a critical bug affects 3.6.3:
https://issues.apache.org/jira/browse/ZOOKEEPER-4712

The buggy method is org.apache.zookeeper.server.ZooKeeperServer.shutdown(boolean). This method is called by ZkServer.shutdown().

Expected behavior

Please update Zookeeper to a newer version.

[junkaixue]

Thanks! But bump up zk is a very risky action. We need to verify and double click on the changes of ZK for the working version.