License correction for libIDL-doc
While converting libIDL to SPDX (LGPLv2+ → LGPL-2.0-or-later), I noticed
that the documentation is actually GPLv3+. The libIDL-doc subpackage’s
License field is therefore corrected from LGPLv2+ to GPL-3.0-or-later.
– Ben Beasley (FAS music)