code: func (s *InteractionsService) UpdateRestrictionsForRepo(ctx context.Context, owner, repo, limit string) (*InteractionRestriction, *Response, error) {
  	u := fmt.Sprintf("repos/%v/%v/interaction-limits", owner, repo)
  
  	interaction := &InteractionRestriction{Limit: String(limit)}
  
  	req, err := s.client.NewRequest("PUT", u, interaction)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	// TODO: remove custom Accept header when this API fully launches.
  	req.Header.Set("Accept", mediaTypeInteractionRestrictionsPreview)
  
  	repositoryInteractions := new(InteractionRestriction)
  
  	resp, err := s.client.Do(ctx, req, repositoryInteractions)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return repositoryInteractions, resp, nil
  }
docs: // UpdateRestrictionsForRepo adds or updates the interaction restrictions for a repository.
  //
  // limit specifies the group of GitHub users who can comment, open issues, or create pull requests
  // for the given repository.
  // Possible values are: "existing_users", "contributors_only", "collaborators_only".
  //
  // GitHub API docs: https://developer.github.com/v3/interactions/repos/#add-or-update-interaction-restrictions-for-a-repository