dev-libs/librelp: Adjusting license to GPL-3+ instead of GPL-3

dev-libs/librelp: Adjusting license to GPL-3+ instead of GPL-3

According to

  - COPYING (every version in tree)
  - src/{lib,}relp.h  (since v1.2.9)

> * Librelp is free software: you can redistribute it and/or modify
> * it under the terms of the GNU General Public License as published by
> * the Free Software Foundation, either version 3 of the License, or
> * (at your option) any later version.

Reported-by: Gokturk Yuksek <gokturk@gentoo.org>
Package-Manager: portage-2.3.0_rc1
Closes: https://github.com/gentoo/gentoo/pull/1658

Signed-off-by: Patrice Clement <monsieurp@gentoo.org>