Make sure we don't get similarly named gems

Was finding the vagrant-chef-zero gem before the actual chef-zero gem:

/home/mike/.vagrant.d/gems/gems/vagrant-chef-zero-0.5.2/bin/chef-zero
/home/mike/.vagrant.d/gems/gems/vagrant-chef-zero-0.5.2/bin/chef-zero

[Chef Zero] Could not find Chef Zero binary in any path in ["/home/mike/.vagrant.d/gems", "/opt/vagrant/bin/../embedded/gems"]