devel/zookeeper: Update to 3.6.2

Changelog: https://zookeeper.apache.org/doc/r3.6.2/releasenotes.html

PR: 250373
Submitted by: Dmitry Wagin <dmitry.wagin@ya.ru> (maintainer)
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D26828