Using script/build since Rakefile no longer exists

# The Problem

The newest version of hub no longer has a Rakefile which makes calling `rake install prefix=path` error out.

# The Solution

Switched the call to `./script/build` and `cp hub "#{node.hub.install_path}"` which results in the intended behaviour.

While updating I noticed it was pointing to the old repo path, so I've updated it here. I've also moved the into an attribute since people might want to pull their own forks.