Timeout is not written to the packet when using Durability

During a review it appears that the durability timeout is not written to the packet as described in Synchronous Durability RFC section "PacketChanges"

Timeout - the second and third optional bytes represent 16-bit unsigned integer, which contains time in milliseconds the durability must be met within, otherwise the mutation will be aborted. If not specified, then a server-defined default is used.

https://github.com/couchbase/couchbase-net-client/blob/master/src/Couchbase/Core/IO/Operations/MutationOperationBase'.cs#L44-L46