Version change (#190)

* [Update] udpate version to 1.5.6

pkg/koko/koko.go

@@ -16,7 +16,7 @@ import (
 	"github.com/jumpserver/koko/pkg/sshd"
 )
 
-const Version = "1.5.5"
+const Version = "1.5.6"
 
 type Coco struct {
 }