code: func (s *ActivityService) ListWatched(ctx context.Context, user string, opt *ListOptions) ([]*Repository, *Response, error) {
  	var u string
  	if user != "" {
  		u = fmt.Sprintf("users/%v/subscriptions", user)
  	} else {
  		u = "user/subscriptions"
  	}
  	u, err := addOptions(u, opt)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	var watched []*Repository
  	resp, err := s.client.Do(ctx, req, &watched)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return watched, resp, nil
  }
docs: // ListWatched lists the repositories the specified user is watching. Passing
  // the empty string will fetch watched repos for the authenticated user.
  //
  // GitHub API docs: https://developer.github.com/v3/activity/watching/#list-repositories-being-watched