Bug 33577: Add btn class to cancel hold button on /reserve/request.pl

Bug 33577: Add btn class to cancel hold button on /reserve/request.pl

To test:
1. Place a hold on a record and look at the /reserve/request.pl page.
2. Notice the two buttons 'Update hold(s)' and 'Cancel selected' buttons are not quite the same size.
3. Apply patch and look again, the buttons should line up.

Signed-off-by: Barbara Johnson <barbara.johnson@bedfordtx.gov>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>