latest joyent centos image

updating to latest joyent centos6 image
```
$ knife joyent image list | grep centos-6 | sort -k 3 | tail -2
26f85622-497a-11e4-ba93-3fe7b89aea1a  centos-6                             20141001    linux    virtualmachine       
f37b10cc-6a9f-11e4-9181-e3d137d947bf  centos-6                             20141112    linux    virtualmachine     
```