Image.ParentCommand and Image.ParentConatiner should be stored

image.go

@@ -19,8 +19,8 @@ type Image struct {
 	Parent          string    `json:"parent,omitempty"`
 	Comment         string    `json:"comment,omitempty"`
 	Created         time.Time `json:"created"`
-	ParentContainer string    `json:-`
-	ParentCommand   []string  `json:-`
+	ParentContainer string    `json:"parent_container,omitempty"`
+	ParentCommand   []string  `json:"parent_command,omitempty"`
 	graph           *Graph
 }