Version bump to 1.3.0

[gescribano]

Hi there,
I destroyed the VM and after a vagrant up I still get a boot2docker vm with docker 1.2 inside.
Do I have to wait until you bump the version to 1.3 ?
I removed my ~/.vagrant.d/boxes/mitchellh-VAGRANTSLASH-boot2docker/

See my log:

mysql: Box 'mitchellh/boot2docker' could not be found. Attempting to find and install...
mysql: Box Provider: virtualbox
mysql: Box Version: >= 0
mysql: Loading metadata for box 'mitchellh/boot2docker'
mysql: URL: https://atlas.hashicorp.com/mitchellh/boot2docker
mysql: Adding box 'mitchellh/boot2docker' (v1.2.0) for provider: virtualbox
mysql: Downloading: https://atlas.hashicorp.com/mitchellh/boxes/boot2docker/versions/1.2.0/providers/virtualbox.box

[ches]

Basically a dupe of #75, I have left a suggestion for you there @gescribano.