Rename API WG -> SIG on specs.openstack.org and in projects.yaml

The repo where the specs live is still labeled 'api-wg' (and there's
no compelling reason to change), but the link on specs.openstack.org
will make more sense for contemporary users with 'API SIG'.

Also update the group's name in projects.yaml

Change-Id: I427267cb0c1a57b56a3d092158d2b4906e096440

gerrit/projects.yaml

@@ -1031,7 +1031,7 @@
     - translate
   description: OpenStack API site
 - project: openstack/api-wg
-  description: API Working Group
+  description: API SIG
   homepage: https://wiki.openstack.org/wiki/API_Working_Group
   groups:
     - openstack-api-wg

specs/specs.yaml

@@ -48,7 +48,7 @@ projects:
   - name: Volume Service Specifications (cinder)
     repo: openstack/cinder-specs
 programs:
-  - name: API Working Group Guidelines
+  - name: API SIG Guidelines
     repo: openstack/api-wg
   - name: Common Libraries Program Specifications (oslo)
     repo: openstack/oslo-specs