Replace d.image with `gmacario/baseimage`

Upstream Docker image `phusion/baseimage` does not contain directory
`/usr/lib/x86_64-linux-gnu/lxc`

which triggers Bug https://github.com/gmacario/vagrant-ubuntu1404/issues/8

Signed-off-by: Gianpaolo Macario <gmacario@gmail.com>
Merge pull request #9 from gmacario/fix-GH-8

Replace d.image with `gmacario/baseimage`