Fix stats examples in README

Change-Id: I1ce91531476ebcc3b6bff226ed40748e54631c2b
Reviewed-on: http://review.couchbase.org/25871
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>