MB-100: fixed dialyzer reported typo

Change-Id: Idd451afb884c4e5c5749f02f0540a325d8b41eee
Reviewed-on: http://review.couchbase.org/25668
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>