Fixes a typo in Architecture
Fixes a typo in Architecture

Closes-bug:#1258606

Change-Id: I61ed701fdf2cc04721ae1093d6ea4b7554870c46
backport: havana

saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,gongysh2004/openstack-manual,AlekhyaMallina-Vedams/openstack-manuals,Akasurde/openstack-manuals,potsmaster/openstack-manuals,openstack/openstack-manuals,saeki-masaki/openstack-manuals,kairoaraujo/openstack-manuals,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,openstack/openstack-manuals,gongysh2004/openstack-manual,openstack/openstack-manuals,openstack/openstack-manuals,potsmaster/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals