code: func (s *RepositoriesService) IsCollaborator(ctx context.Context, owner, repo, user string) (bool, *Response, error) {
  	u := fmt.Sprintf("repos/%v/%v/collaborators/%v", owner, repo, user)
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return false, nil, err
  	}
  
  	resp, err := s.client.Do(ctx, req, nil)
  	isCollab, err := parseBoolResponse(err)
  	return isCollab, resp, err
  }
docs: // IsCollaborator checks whether the specified GitHub user has collaborator
  // access to the given repo.
  // Note: This will return false if the user is not a collaborator OR the user
  // is not a GitHub user.
  //
  // GitHub API docs: https://developer.github.com/v3/repos/collaborators/#get