ZOOKEEPER-4298: Update http to https in zoo_sample.cfg

Author: lan <liaonan@souche.com>

Reviewers: maoling <maoling@apache.org>

Closes #1699 from lanicc/ZOOKEEPER-4298

conf/zoo_sample.cfg

@@ -19,7 +19,7 @@ clientPort=2181
 # Be sure to read the maintenance section of the 
 # administrator guide before turning on autopurge.
 #
-# http://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_maintenance
+# https://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_maintenance
 #
 # The number of snapshots to retain in dataDir
 #autopurge.snapRetainCount=3