定义模型的观察者 make:observer 未定义是怎么回事

这是我输入的命令

$ php artisan make:observer UserObserver --model=User

下面是命令行返回的命令

Command "make:observer" is not defined.

  Did you mean one of these?
      make:auth
      make:command
      make:controller
      make:event
      make:exception
      make:factory
      make:job
      make:listener
      make:mail
      make:middleware
      make:migration
      make:model
      make:notification
      make:policy
      make:provider
      make:request
      make:resource
      make:rule
      make:seeder
      make:test

这是什么问题，命令不存在么？