Update CentOS 6.4 box.

CentOS 6.4 x86_64 Minimal (2014-01-16)

Highlights of this release:

  * Fix for swap drive not being automatically mounted.
  * Put the swap drive on a separate disk.
  * Lock the kernel version a different way so plugins like
    `vagrant-vbguest` can upgrade VirtualBox Guest Additions.
  * Improved shell script cross compatibility.
  * Reduced the size of the initramfs.
  * The final cleanup operation performed before distribution should
    now be faster.