Set correct designate endpoint in docs

Change-Id: Id2ecf65f3e5afef9b6231565cac2d797650e38a7
Closes-Bug: #1726726

Author: zaneb

doc/source/cli/plugin-commands.rst

@@ -32,7 +32,7 @@ congress
 designate
 ---------
 
-.. list-plugins:: openstack.dns.v1
+.. list-plugins:: openstack.dns.v2
    :detailed:
 
 gnocchi