Use GPL v1 like Perl and PDL.

[sebastic]

The license mentioned in the source refers to GPL v2, but refers to https://dev.perl.org/licenses/ for more information which documents the Perl (and PDL) license as GPL v1 (or later) or the Artistic License.

This PR corrects the license mentioned in the README and source as GPL v1 to match Perl and PDL.

[coveralls]

Pull Request Test Coverage Report for Build 12813250583

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 55.417%

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Totals
Change from base Build 11546848050:	0.0%
Covered Lines:	578
Relevant Lines:	1043

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💛 - Coveralls