Fix typo in public security domain section
Fix typo in public security domain section

Change-Id: I9a2096333089b9714c0f8a688fbe30b4371b40c0
Implements: blueprint arch-guide

openstack/openstack-manuals,Akasurde/openstack-manuals,kairoaraujo/openstack-manuals,potsmaster/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,Akasurde/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,kairoaraujo/openstack-manuals,potsmaster/openstack-manuals,saeki-masaki/openstack-manuals