Copyright for r-cran-bit64 source package in Bionic

Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
Upstream-Name: bit64
Upstream-Contact: Jens Oehlschlägel 
Source: https://cran.r-project.org/package=bit64

Files: *
Copyright: Jens Oehlschlägel 
License: GPL-2

Files: debian/*
Copyright: 2017 Andreas Tille 
License: GPL-2

License: GPL-2
 On Debian systems you can find the full text of the GNU General Public
 License at /usr/share/common-licenses/GPL-2.