code: func (s *UsersService) IsFollowing(ctx context.Context, user, target string) (bool, *Response, error) {
  	var u string
  	if user != "" {
  		u = fmt.Sprintf("users/%v/following/%v", user, target)
  	} else {
  		u = fmt.Sprintf("user/following/%v", target)
  	}
  
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return false, nil, err
  	}
  
  	resp, err := s.client.Do(ctx, req, nil)
  	following, err := parseBoolResponse(err)
  	return following, resp, err
  }
docs: // IsFollowing checks if "user" is following "target". Passing the empty
  // string for "user" will check if the authenticated user is following "target".
  //
  // GitHub API docs: https://developer.github.com/v3/users/followers/#check-if-you-are-following-a-user