donate: fix link to the about page
donate: fix link to the about page

The problem was noticed by Jeroen van Rijn <jvrnix@gmail.com>, but a
different fix was needed to make things work properly.

Thanks Jeroen for noticing and reporting the problem!

Signed-off-by: Thomas Petazzoni <a5d87d2bd7c424ee5cbdb4e978635bf653d5a005@enix.org>

maposmatic/maposmatic,hholzgra/maposmatic,hholzgra/maposmatic,maposmatic/maposmatic,hholzgra/maposmatic,hholzgra/maposmatic,hholzgra/maposmatic,maposmatic/maposmatic,maposmatic/maposmatic