Update centos-art.sh script copyright holder.
- Previously, we were using The CentOS Project as copyright holder for
centos-art.sh script. The CentOS Project main goal is The CentOS
Distribution not the centos-art.sh script. The centos-art.sh script
exists to automate frequent tasks inside The CentOS Artwork
Repository which is the main goal of The CentOS Artwork SIG. In this
sake, The CentOS Artwork SIG is closer than The CentOS Project and
should be used, instead. This update changes centos-art.sh scripts
and set The CentOS Artwork SIG as copyright holder.