Update URL for openstack zuul example

Change-Id: Iae253977eafaff1a7cbdcaf1b873388487c4e36e
Signed-off-by: Paul Belanger <paul.belanger@polybeacon.com>
Reviewed-on: https://review.openstack.org/21730
Reviewed-by: Elizabeth Krumbach <lyz@princessleia.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins