update version number to 1.6.0 to match ambari-serer version
update version number to 1.6.0 to match ambari-serer version

jagatsingh/ambari-rest-client,sequenceiq/ambari-rest-client,dlyle65535/ambari-rest-client,jagatsingh/ambari-rest-client,dlyle65535/ambari-rest-client,sequenceiq/ambari-rest-client