Vagrant cannot install nokogiri-dependent plugins

Question

I\'m trying to install the rackspace plugin for vagrant (1.5.1):

vagrant plugin install vagrant-rackspace

But it complains

Answer 1

If Nate Murray's solution doesn't work, I found upgrading to a Vagrant version > 1.6.4 fixed the issue (as noted in this Github issue: https://github.com/mitchellh/vagrant/issues/3769)