Github user jtstorck commented on the issue:
https://github.com/apache/nifi/pull/2884
@joewitt I brought up the upgrade a while ago, but many of the
services/components we integrate with are using Zookeeper 3.4.6. Originally I
wanted to use a newer version that did not explicitly depend on log4j, because
it was causing some issues with the NiFi Toolkit. Since we were able to work
around the dependency issue, we didn't upgrade the version.---
