Copyright for r-cran-devtools source package in Bionic

Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
Upstream-Name: devtools
Upstream-Contact: Hadley Wickham 
Source: https://cran.r-project.org/package=devtools

Files: *
Copyright: 2010-2017 Hadley Wickham, Winston Chang, RStudio
License: GPL-2+

Files: debian/*
Copyright: 2018 Andreas Tille 
License: GPL-2+

License: GPL-2+
    This program 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 2 of the License, or
    (at your option) any later version.
 .
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
 .
 On Debian systems you can find the full text of GNU General Public
 License version 2 or later at /usr/share/common-licenses/GPL-2.