It looks like you need to upgrade the VM after installing boot2docker:
if you are upgrading from boot2docker 0.12 or later, you can update your existing virtual machine (after upgrading using the installer) using boot2docker stop && boot2docker download && boot2docker up – and you will not lose your existing data.
(https://github.com/boot2docker/osx-installer/releases/tag/v1.1.0)