License change for stockfish: GPLv3+ -> GPLv3+ and CC0

[Ondrej Mosnacek]

Hi,

The stockfish package will start building from an additional source
file containing trained neural network weights, which is provided
under the Creative Commons Zero license.

See the pending pull request for more details:
https://src.fedoraproject.org/rpms/stockfish/pull-request/1

-- 
Ondrej Mosnacek
Software Engineer, Linux Security - SELinux kernel
Red Hat, Inc.