Fix Member struct for organization member.

[fnaoto]

Fix response from deploygate.
Please review this PR when you have enough time. 😃

reference URL:

• https://docs.deploygate.com/reference#organizations-members-index

200 response sample below.

{
  "error": false,
  "members": [
    {
      "type": "User",
      "name": "foo",
      "icon_url": "https://secure.gravatar.com/avatar/foo",
      "url": "https://deploygate.com/users/foo"
    },
    {
      "type": "User",
      "name": "invitee@test.com",
      "icon_url": "https://secure.gravatar.com/avatar/default",
      "inviting": true,
      "url": "https://deploygate.com/users/invitee@test.com"
    }
  ]
}