ssh://git@github.com doesn't match LibGit2.GITHUB_REGEX

[tkoolen]

URLs of the form ssh://git@github.com/tkoolen/PlanarConvexHulls.jl.git (prevalent with Pkg.setprotocol!("ssh")) don't match LibGit2.GITHUB_REGEX, which e.g. causes issues with DocumenterTools.Travis.genkeys.