Fix release mapping (19.1 -> 20.0)
Fix release mapping (19.1 -> 20.0)

We have some backward incompatible changes, so we need a major bump
See [1] for more details

[1] https://zuul.opendev.org/t/openstack/build/e5174d1d8d68491aa01d9a2e3e020a4b/log/tox/list-changes-results.log#1932-1944

Change-Id: Ia3fb13d7f6c29904cf9e1ffe446e3473fdbeecef

openstack/ironic,openstack/ironic