Should handle forks gracefully

[JAForbes]

When forking a package, you may want to still publish to npm for the fork, but without editing package.json as you expect to upstream your changes eventually.

pr-release should probably default to ignoring the package.json name when publishing from a fork, and instead use the github repo path e.g. JAForbes/pr-release becomes jaforbes-pr-release.

I think this behaviour should be opt out instead of opt in because we're trying to avoid changes to source in the fork that are unrelated to legit enchancements or bug fixes.

Maybe the opt out can occur via env variable, or maybe just a flag like --no-forks to opt out.

Need to think about that one.