fix rpmspec to use cmake package on CentOS 8
fix rpmspec to use cmake package on CentOS 8

Change-Id: Ieaf83d922495b7f8f8ea790e3c05c3fc45de1432
Reviewed-on: http://review.couchbase.org/c/libcouchbase/+/155641
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Sergey Avseyev <87f6d5e4fd3644c3c20800cde7fd3ad1569370b3@gmail.com>

couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase