Update default configs to use https://demo.dspace.org/server/

config/config.example.yml

@@ -22,7 +22,7 @@ ui:
 # 'synced' with the 'dspace.server.url' setting in your backend's local.cfg.
 rest:
   ssl: true
-  host: sandbox.dspace.org
+  host: demo.dspace.org
   port: 443
   # NOTE: Space is capitalized because 'namespace' is a reserved string in TypeScript
   nameSpace: /server

config/config.yml

@@ -1,5 +1,5 @@
 rest:
   ssl: true
-  host: sandbox.dspace.org
+  host: demo.dspace.org
   port: 443
   nameSpace: /server

docker/docker-compose-dist.yml

@@ -24,7 +24,7 @@ services:
       # This is because Server Side Rendering (SSR) currently requires a public URL,
       # see this bug: https://github.com/DSpace/dspace-angular/issues/1485
       DSPACE_REST_SSL: 'true'
-      DSPACE_REST_HOST: sandbox.dspace.org
+      DSPACE_REST_HOST: demo.dspace.org
       DSPACE_REST_PORT: 443
       DSPACE_REST_NAMESPACE: /server
     image: dspace/dspace-angular:dspace-7_x-dist