Update the license_list.go to have more permissible inputs for greater SPDXID matching.
EX:
GPL3 gpl3 gpl-3 and GPL-3 can all map to GPL-3.0-only
By moving all strings to lower and removing the "-" we're able to return valid SPDX license ID for a greater diversity of input strings.
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Signed-off-by: Christopher Phillips <christopher.phillips@anchore.com>
