Spacebars are missed in ServiceDependence.toString()

[Alexey Fedorov]

Hi all,

I am playing with Jigsaw and found the following small bug: method 
ServiceDependence.toString() contains modifier without any spacebars 
between them.

Set<Dependence.Modifier> modifiers = new 
HashSet<>(Arrays.asList(OPTIONAL, PUBLIC));
ServiceDependence sd = new ServiceDependence(modifiers, "my.service");

sd.toString returns:

> requires serviceoptionalpublic my.service

but expected something like:

> requires service optional public my.service

Seems like small bug :)

--
Thank you,
Alexey