Update env.sh.example

Update env.sh.example configuration file to use ZooKeeper 3.6.2
diff --git a/conf/env.sh.example b/conf/env.sh.example
index 1f1461b..9691521 100644
--- a/conf/env.sh.example
+++ b/conf/env.sh.example
@@ -40,7 +40,7 @@
 # Versions set below will be what is included in the shaded jar
 export ACCUMULO_VERSION="`$ACCUMULO_HOME/bin/accumulo version`"
 export HADOOP_VERSION="`hadoop version | head -n1 | awk '{print $2}'`"
-export ZOOKEEPER_VERSION=3.4.13
+export ZOOKEEPER_VERSION=3.6.2
 # Path to shaded test jar
 ex_home=$( cd "$( dirname "$conf_dir" )" && pwd )
 export EXAMPLES_JAR_PATH="${ex_home}/target/accumulo-examples-shaded.jar"