license_groups: add VIGRA to @BINARY-REDISTRIBUTABLE

license_groups: add VIGRA to @BINARY-REDISTRIBUTABLE

As discussed in #gentoo-releng on 2019/04/22 and in bug 684126.

The VIGRA license, which is based on Artistic(-1):
- permits distribution
- does not require explicit approval
- does not restrict cost of redistribution**

** The Artistic(-1) license already permits a reasonable copying fee, and is
still @OSI-APPROVED, but not @FSF-APPROVED. Artistic-2 clarifies the
language of the copying fee as "Distributor Fee", but still permits it,
and is @GPL-COMPATIBLE.

Fixes: https://bugs.gentoo.org/684126
Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>