Switch to the new canonical constraints URL on master
Switch to the new canonical constraints URL on master

Reference:
1. http://lists.openstack.org/pipermail/openstack-discuss/2019-May/006478.html
2. https://review.opendev.org/#/c/601188

Change-Id: I011457f4f2548d14ebea0e7671c34ec53ec86461

openstack/watcher-dashboard,openstack/watcher-dashboard,openstack/watcher-dashboard,openstack/watcher-dashboard