Fixes introduced error running vagrant hostmanager command

lib/vagrant-hostmanager/action/update_guest.rb

@@ -11,6 +11,14 @@ module VagrantPlugins
           @machine = env[:machine]
           @global_env = @machine.env
           @provider = env[:provider]
+
+          # config_global is deprecated from v1.5
+          if Gem::Version.new(::Vagrant::VERSION) >= Gem::Version.new('1.5')
+            @config = @global_env.vagrantfile.config
+          else
+            @config = @global_env.config_global
+          end
+          
           @logger = Log4r::Logger.new('vagrant::hostmanager::update_guest')
         end