Use NFS for Vagrant shared folder

Apparently the default VirtualBox file system used for shared folders
has a really weird bug that prevents repo cloning from working. Yup,
this was a blast to debug. Using NFS for the share fixes (?) this.

Discussion: libgit2/git2go#194

Vagrantfile

@@ -8,7 +8,8 @@ Vagrant.configure(2) do |config|
   config.vm.hostname = "evabox"
   config.vm.define "evabox"
   config.vm.box_check_update = false
-  config.vm.synced_folder '.', '/evabot'
+  config.vm.synced_folder '.', '/evabot', nfs: true
+  config.vm.network "private_network", type: "dhcp"
   config.vm.network "forwarded_port", guest: 3000, host: 3000
 
   config.vm.provider "virtualbox" do |v|