Windows don't support the %zu formatter

Change-Id: Ia36bc151f84af9cfd6c069c3d97c494753d449f3
Reviewed-on: http://review.couchbase.org/40650
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>