API: Repository ID type has changed from string to int

Repositories are documented as having ID of type integer - https://developer.travis-ci.com/resource/repository#standard-representation

This commit has resulted in the ID possibly being a string - when POSTing to /repo/{repository.slug}/requests, we get this back:

{
  "request": {
    "repository": {
      "id": "181942726", 
      "vcs_type": "GithubRepository",
      ...
    }
  }
}
Imprint