Let Dependency.toString() print if an optional dependency is marked as default.
Let Dependency.toString() print if an optional dependency is marked as default.

jeanbaptistelab/dub,Geod24/dub,rjframe/dub,Flamaros/dub,p0nce/dub,grogancolin/dub,jelmansouri/dub,D-Programming-Language/dub,gedaiu/dub