Fix plugin install

Author: pascal

vagrant/vagrant.rb

@@ -14,7 +14,7 @@
 # We currently use only one plugin, so skip iterating.
 def vagrant_ensure_plugins
   plugin = 'vagrant-hostsupdater'
-  return unless config_get_item('skip_vagrant_plugins_check') == true
+  return if config_get_item('skip_vagrant_plugins_check') == true
   system "vagrant plugin install #{plugin}" unless Vagrant.has_plugin? plugin.to_s
 end