puppet: Add another missing dependency on postgresql-common

The postgres group must exist before we give files to it.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

puppet/zulip/manifests/postgres_common.pp

@@ -37,6 +37,7 @@ class zulip::postgres_common {
     group => "postgres",
     mode => 750,
     source => "puppet:///modules/zulip/postgresql/env-wal-e",
+    require => Package["postgresql-${zulip::base::postgres_version}"],
   }
 
   file { "/usr/local/bin/pg_backup_and_purge.py":