Bug#839205: openorienteering-mapper: New version available on Github

[Kai Pastor, DG0YT]

Package: openorienteering-mapper
Version: 0.6.3-2

Dear Maintainer,
OpenOrienteering Mapper is developed on Github
(https://github.com/OpenOrienteering/mapper/).
The current release is 0.6.5.
The watch file in Debian needs to be corrected to point to Github 
instead of Sourceforge.

Thanks.