Cleaning up tree.go per gofmt and go vet
diff --git a/cmd/tree.go b/cmd/tree.go
index 98435fd..0a276fd 100644
--- a/cmd/tree.go
+++ b/cmd/tree.go
@@ -64,7 +64,7 @@
 
 	sortable := make([]string, len(direct))
 	i := 0
-	for k, _ := range direct {
+	for k := range direct {
 		sortable[i] = k
 		i++
 	}