Allow the Vagrantfile to be tracked as that's the intended purpose.

From the documentation at http://docs.vagrantup.com/v2/getting-started/project_setup.html

"The Vagrantfile is meant to be committed to version control with your project, if you use version control. This way, every person working with that project can benefit from Vagrant without any upfront work."

Global/Vagrant.gitignore

 .vagrant/
-Vagrantfile