you can specify version as
docker run -d --name db-cb -p 8091-8094:8091-8094 -p 11210-11211:11210-11211 couchbase:4.6.3
Due to some internet issue, below command was not working. So i got impression that it's not the right command.
Below command works -
docker run -d --name db-cb -p 8091-8094:8091-8094 -p 11210-11211:11210-11211 couchbase:enterprise-4.6.3