Authors should have 2 more fields

[Ritarira]

When a request is made to get a list of authors or to get a single author the time stamps should be shown.

Current behaviour Request: GET localhost:3000/authors/9

Response: Status 200

{
    "id": 9,
    "first_name": "Sally",
    "last_name": "Thorne",
    "books_count": 0
}

Expected behaviour Request: GET localhost:3000/authors/9

Response: Status 200

{
    "id": 9,
    "first_name": "Sally",
    "last_name": "Thorne",
    "books_count": 0
    "created_at": "2017-12-04T07:30:35.820Z",
    "updated_at": "2017-12-07T07:12:09.566Z"
}