MB-8791: fixed typo in the errors text

Change-Id: I526d168d3c227e3377eeb86a21c9cf67fa194702
Reviewed-on: http://review.couchbase.org/28348
Reviewed-by: Pavel Blagodov <stochmail@gmail.com>
Tested-by: Pavel Blagodov <stochmail@gmail.com>