Laravel Homestead不承认环境变量

Question

所以，这是我的Homestead.yaml文件：

---
ip: "192.168.10.10"
memory: 2048
cpus: 1

authorize: ~/.ssh/id_rsa.pub

keys:
    - ~/.ssh/id_rsa

folders:
    - map: ~/Projects
      to: /home/vagrant/Projects

sites:
    - map: laravel
      to: /home/vagrant/Projects/laravel/public

databases:
    - homestead

variables:
    - key: db_host
      value: localhost
    - key: db_database
      value: homestead
    - key: db_username
      value: homestead
    - key: db_password
      value: secret

但是，我一直收到一条错误，说Undefined index: db_host，这里可以看到：

我做错了什么？