change vagrant version

Vagrantfile

@@ -3,7 +3,7 @@
 
 require 'fileutils'
 
-Vagrant.require_version ">= 1.9.0"
+Vagrant.require_version ">= 2.0.0"
 
 CONFIG = File.join(File.dirname(__FILE__), "vagrant/config.rb")
 
@@ -135,12 +135,6 @@ Vagrant.configure("2") do |config|
 
       config.vm.network :private_network, ip: ip
 
-      # workaround for Vagrant 1.9.1 and centos vm
-      # https://github.com/hashicorp/vagrant/issues/8096
-      if Vagrant::VERSION == "1.9.1" && $os == "centos"
-        config.vm.provision "shell", inline: "service network restart", run: "always"
-      end
-
       # Disable swap for each vm
       config.vm.provision "shell", inline: "swapoff -a"
 

docs/vagrant.md

 Vagrant Install
 =================
 
-Assuming you have Vagrant (1.9+) installed with virtualbox (it may work
+Assuming you have Vagrant (2.0+) installed with virtualbox (it may work
 with vmware, but is untested) you should be able to launch a 3 node
 Kubernetes cluster by simply running `$ vagrant up`.<br />