updated `Vagrantfile` from latest in `flutterbye` repository.

Vagrantfile

@@ -1,8 +1,6 @@
 # -*- mode: ruby -*-
 # vi: set ft=ruby :
 
-require "rbconfig"
-
 # Vagrant configuration (https://docs.vagrantup.com)
 
 Vagrant.configure("2") do |config|
@@ -12,15 +10,34 @@ Vagrant.configure("2") do |config|
       #vb.gui = true
       vb.memory = "2048"
       override.vm.box = "debian/contrib-jessie64"
+      # the `vagrant-vbguest` plugin can fail when the guest tools installation
+      # prompts for confirmation, so we need to ensure it's not interactive.
+      if Vagrant.has_plugin? "vagrant-vbguest" then
+         config.vbguest.installer_arguments = "--nox11 -- --force"
+      end
    end
 
-   # the docker provider is preferable to the virtualbox provider,
-   # but seems to only work properly on linux.
+   # WARNING: vagrant's hyper-v support appears to work infrequently. virtualbox
+   # integration is more reliable (ymmv).
+   config.vm.provider "hyperv" do |hyperv, override|
+      #hyperv.gui = true
+      hyperv.memory = "2048"
+      # `hashicorp/precise64` hit a roadblock when trying to compile ocaml, so
+      # an alternative box with a newer distro needed to be used.
+      override.vm.box = "nikel/xerus64"
+   end
+
+   # docker appears to be an unpopular vagrant provider (the most popular box
+   # has only 184 downloads at the moment this sentence is being written!). i
+   # prefer the docker provider to more heavyweight virtualization providers,
+   # however, but the docker provider seems to only work properly on linux.
    config.vm.provider "docker" do |d, override|
+      # NOTE: you may need to manually pull this box before issuing a
+      #`vagrant up --provider=docker` on older versions of vagrant.
       override.vm.box = "tknerr/baseimage-ubuntu-16.04"
    end
 
-    config.vm.network "forwarded_port", guest: 8888, host: 8888, auto_correct: true
+   config.vm.network "forwarded_port", guest: 8888, host: 8888, auto_correct: true
 
    config.vm.provision "shell", inline: <<-SHELL
       /bin/sh /vagrant/scripts/setup/vagrant.sh