adding user command to switch

pkg/commands/commands.go

@@ -50,6 +50,8 @@ func GetCommand(cmd instructions.Command, buildcontext string) (DockerCommand, e
 		return &EntrypointCommand{cmd: c}, nil
 	case *instructions.LabelCommand:
 		return &LabelCommand{cmd: c}, nil
+	case *instructions.UserCommand:
+		return &UserCommand{cmd: c}, nil
 	}
 	return nil, errors.Errorf("%s is not a supported command", cmd.Name())
 }