Refactor spec with official API schema

[sue445]

ChatWork API provides API schema written by RAML
https://github.com/chatwork/api/blob/master/RAML/api-ja.raml

So I used response example in RAML as test response

e.g. https://github.com/chatwork/api/blob/21970e7f86f0cc0f7179f1f24b6529013fca7dab/RAML/api-ja.raml#L827-L839

              example: |
                [
                  {
                    "account_id": 123,
                    "role": "member",
                    "name": "John Smith",
                    "chatwork_id": "tarochatworkid",
                    "organization_id": 101,
                    "organization_name": "Hello Company",
                    "department": "Marketing",
                    "avatar_image_url": "https://example.com/abc.png"
                  }
                ]