Why its not working with negative weights ?

[berktaylan]

`g.addEdge(new jsgraphs.Edge(0,1,1));
g.addEdge(new jsgraphs.Edge(1,0,-1));

g.addEdge(new jsgraphs.Edge(1,2,1));
g.addEdge(new jsgraphs.Edge(2,1,-1));

g.addEdge(new jsgraphs.Edge(2,3,1));
g.addEdge(new jsgraphs.Edge(3,2,-1));

g.addEdge(new jsgraphs.Edge(3,1,1));
g.addEdge(new jsgraphs.Edge(1,3,-1));`