Suggestion: adjustment for license filename match

It seems like `<prefix>-LICENSE.txt` is a not-totally-uncommon format for license filenames; for example: `MIT-LICENSE.txt` or `GPL-LICENSE.txt`. Perhaps it'd be possible to adjust the filename matching to permit finding more license files. Figuring out why a license wasn't being found involved a bunch of debugging that pinpointed the regex responsible, so I'll also offer a pull request with a potential changeset alongside this request.