packaging: use upper-case URL tag in RPM
packaging: use upper-case URL tag in RPM

Either "Url:" or "URL:" works, but the Fedora project has standardized
on "URL:"

Signed-off-by: Ken Dreyer <940dddfbf8b0685439b7ecf27daa0ba58b359a2c@redhat.com>

ceph/radosgw-agent,ceph/radosgw-agent