logstash service: fix startup

Changed files
+1
nixos
modules
services
logging
+1
nixos/modules/services/logging/logstash.nix
···
description = "Logstash Daemon";
wantedBy = [ "multi-user.target" ];
environment = { JAVA_HOME = jre; };
+
path = [ pkgs.bash ];
serviceConfig = {
ExecStart =
"${cfg.package}/bin/logstash agent " +