Fix cpanfile git syntax

[zmughal]

Uses git + ref options, not branch: https://github.com/oberth-manoeuvre/p5-Oberth-Launch/blob/7826a887553d30feba13bbf01e340a3a7b909325/lib/Oberth/Launch.pm#L188

• https://metacpan.org/pod/App::cpm::Tutorial#cpanfile-and-dist/url/mirror/git-syntax
• https://github.com/miyagawa/cpanfile/blob/1.1004/t/requirement.t