Don't print all databases during entrypoint check

docker-entrypoint.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 set -e
 
-until psql $DATABASE_URL -c '\l'; do
+until psql $DATABASE_URL -c '\q'; do
   >&2 echo "Postgres is unavailable - sleeping"
   sleep 1
 done