FIX license code regression

* Updated 'artistic' and 'artistic_2' valid license names to valid CPAN::Meta Spec 2.0 strings
* BUG was causing CPAN::Meta exceptions when constructing META files

The refactored license code (_get_license()) fails for artistic and artistic_2 licenses.

The refactored license code causes an exception during META file generation (within CPAN::Meta) when using the 'artistic' or 'artistic_2' licenses. The license names listed do not match the CPAN::Meta 2.0 spec
(see URLref: http://search.cpan.org/~dagolden/CPAN-Meta-2.133380/lib/CPAN/Meta/Spec.pm#license).

This BREAKS any author build using either license.

The attached patch fixes the problem but no longer matches the name of the Software::License::($NAME).pm (see URL: http://cpansearch.perl.org/src/RJBS/Software-License-0.103008/lib/Software/License). I'm not sure if that's a problem. If so, is it a bug in the CPAN::Meta spec or the Software::License code?