code: func (s *ActivityService) GetThreadSubscription(ctx context.Context, id string) (*Subscription, *Response, error) {
  	u := fmt.Sprintf("notifications/threads/%v/subscription", id)
  
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	sub := new(Subscription)
  	resp, err := s.client.Do(ctx, req, sub)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return sub, resp, nil
  }
docs: // GetThreadSubscription checks to see if the authenticated user is subscribed
  // to a thread.
  //
  // GitHub API docs: https://developer.github.com/v3/activity/notifications/#get-a-thread-subscription