Bug#960517: Reflect Trac -> GitHub migration in copyright file

[積丹尼 Dan Jacobson]

Package: gdal-bin
Version: 3.0.4+dfsg-1+b6
Severity: minor

https://github.com/OSGeo/gdal is only mentioned on
$ rgrep https://github.com/OSGeo/gdal -l /usr/share/doc/*gdal*/
/usr/share/doc/libgdal-doc/gdal/ogr_feature_style.html
/usr/share/doc/libgdal-doc/gdal/menudata.js
/usr/share/doc/libgdal-doc/gdal/credits.html
/usr/share/doc/libgdal-doc/gdal/index.html

It should be mentioned on more (but not all) of
$ find /usr/share/doc/*gdal*/copy*
/usr/share/doc/gdal-bin/copyright
/usr/share/doc/gdal-data/copyright
/usr/share/doc/libgdal-doc/copyright
/usr/share/doc/libgdal-grass/copyright
/usr/share/doc/libgdal-perl-doc/copyright
/usr/share/doc/libgdal-perl/copyright
/usr/share/doc/libgdal26/copyright
/usr/share/doc/python3-gdal/copyright

Instead of only their older
http://trac.osgeo.org/gdal/