fixed language in couple of error messages

Change-Id: I44aa777769df4c6306a19e76718c2a34e99a9faf
Reviewed-on: http://review.couchbase.org/38469
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>