Update vm.box name to precise64

`precise64` is a standard box that almost everyone already has is his
machines with http://files.vagrantup.com/precise64.box url content.

Forcing user to download the same box only with a different name is not a
good thing.

Signed-off-by: Rogerio Prado de Jesus <rogeriopradoj@gmail.com>
Merge pull request #1 from rogeriopradoj/change-box-name-for-precise64

Update vm.box name to precise64