code: func (s *UsersService) IsBlocked(ctx context.Context, user string) (bool, *Response, error) {
  	u := fmt.Sprintf("user/blocks/%v", user)
  
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return false, nil, err
  	}
  
  	// TODO: remove custom Accept header when this API fully launches.
  	req.Header.Set("Accept", mediaTypeBlockUsersPreview)
  
  	resp, err := s.client.Do(ctx, req, nil)
  	isBlocked, err := parseBoolResponse(err)
  	return isBlocked, resp, err
  }
docs: // IsBlocked reports whether specified user is blocked by the authenticated user.
  //
  // GitHub API docs: https://developer.github.com/v3/users/blocking/#check-whether-youve-blocked-a-user