testing/goxel: upgrade to 0.15.1
https://github.com/guillaumechereau/goxel/releases/tag/v0.15.1
https://github.com/guillaumechereau/goxel/releases/tag/v0.15.0
Readded gtk+3.0-dev
as pkgconfig now looks for it.
Edited by mio
https://github.com/guillaumechereau/goxel/releases/tag/v0.15.1
https://github.com/guillaumechereau/goxel/releases/tag/v0.15.0
Readded gtk+3.0-dev
as pkgconfig now looks for it.