Remove compile warning

The format specifier for 64 bit integers caused warning

Change-Id: Ia9dda08d0251cedbdfab3ab286ea430f35afe843
Reviewed-on: http://review.couchbase.org/28692
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>