fix incorrent email address

pgadmin does not start in newer versions if the
provided email address is not valid

docker-compose.yml

@@ -60,7 +60,7 @@ services:
     restart: always
     environment:
       PGADMIN_DEFAULT_PASSWORD: clubmate42
-      PGADMIN_DEFAULT_EMAIL: icebox
+      PGADMIN_DEFAULT_EMAIL: icebox@nobreakspace.org
   database:
     image: postgres
     restart: always