course fetchAll

GET /api/courses

返回

{
  "code": 1,
  "msg": "SUCCESS",
  "data": [
    {
      "id": "5b29e61cca51891746b20206",
      "title": "title",
      "coverImg": "asdasdsad",
      "direction": 1,
      "type": [0, 1, 2],
      "difficulty": 0,
      "price": 10,
      "sections": [
        {
          "title": "title"
        }
      ]
    }
  ]
}