Use KeyVersions instead of Mutation from common

Mutation struct has been renamed to KeyVersions in common.
Use the latest one.

Change-Id: Ib31de86456a2425398d9c7dd630f872d66a15b00
Reviewed-on: http://review.couchbase.org/38141
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Tested-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>