change edge weight attribute to len

cmd/internal/graph/dot/nodes_edges.go

@@ -54,7 +54,7 @@ func (e *weightedLine) SetAttribute(attr encoding.Attribute) error {
 	var err error
 
 	switch attr.Key {
-	case "weight":
+	case "len":
 		e.W, err = strconv.ParseFloat(attr.Value, 64)
 	default:
 		err = errors.New("unknown key:" + attr.Key)