Update links to the registry and API.
Update links to the registry and API.

The locations moved from www.usa.gov to  socialmobileregistrydigital.gov
GSA/social-media-registry,GSA/social-media-registry,GSA/social-media-registry,ctacdev/social-media-registry,ctacdev/social-media-registry,ctacdev/social-media-registry,ctacdev/social-media-registry,GSA/social-media-registry