What I've encountered:

1. on CentOS 6.5 & CentOS 7
2. yum install rpm-build
3. got rpm-build.x86_64 0:4.11.3-17.el7
4. wget https://github.com/martinh/libconfuse/releases/download/v3.0/confuse-3.0.tar.gz
5. rpmbuild -tb confuse-3.0.tar.gz
6. got error error: line 32: Unknown tag: Copyright: ISC

Please consider to change

Copyright: ISC
at line 32 ./libconfuse.spec to
License: ISC
since Copyright tag has been deprecated for a long time