Change to precise64-10g box

The Vagrantfile now references a 10GB precise64 box.

I created this box by starting with the 80GB precise64 box at http://files.vagrantup.com/precise64.box.

I attached the VMDK to an Ubuntu VM, and shrank the filesystem using `resize2fs` and `lvreduce` (as mentioned here: http://blog.shadypixel.com/how-to-shrink-an-lvm-volume-safely/).

Then, I verified the vagrant vm booted up with the resized box, ran `vagrant package` to produce a .box file, and posted it to Dropbox.
Merge pull request #6 from datadryad/box-size-10g

Change to precise64-10g box