chore(*): add minimum version requirement to Vagrantfile
correction regarding providers

I'm pretty sure this is what you meant
pedantic capitalization fixes: VirtualBox & VMware

The capitalization they each use on their respective web sites is [VirtualBox](https://www.virtualbox.org/) and [VMware](http://www.vmware.com/) (ignoring when it's part of their logotype, in which case it's all lowercase).

I left one example of "Virtualbox" to avoid a merge conflict with my other pull request.  (I'm assuming you'll accept that one, but if you don't, and accept only this, then you'll want to manually fix that.... or I can send a third if you'd like.)
Merge pull request #135 from brandondrew/patch-1

correction regarding providers
Merge pull request #136 from brandondrew/patch-2

pedantic capitalization fixes: VirtualBox & VMware
Merge pull request #133 from jonboulle/master

add minimum version requirement to Vagrantfile
Added warning about token refreshing
Merge pull request #140 from bobrik/patch-1

Added warning about token refreshing