cli doesn't like memory optimized

This CLI worked without memory optimized, but adding it makes the CLI fail.

root@ip-10-0-0-58 ~]# /opt/couchbase/bin/couchbase-cli cluster-init \
> -c 127.0.0.1:8091 --cluster-username=Administrator \
> --cluster-password=password \
> --cluster-init-ramsize=18432 \
> --services=data,index,query \
> --cluster-index-ramsize=34816 \
> --index-storage-setting=memopt
{"errors":{"storageMode":"storageMode must be one of forestdb, memory_optimized"}}
[root@ip-10-0-0-58 ~]# /opt/couchbase/bin/couchbase-cli cluster-init -c 127.0.0.1:8091 --cluster-username=Administrator --cluster-password=password --cluster-init-ramsize=18432 --services=data,index,query --cluster-index-ramsize=34816 --index-storage-setting=memory_optimized
ERROR: invalid index storage setting `memory_optimized`. Must be [default, memopt]