Update Couchbase::VERSION to 1.2.3

Change-Id: Ib8a412d0c2979468955f9493b924e7be165689c2
Reviewed-on: http://review.couchbase.org/25449
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>