Update cirros
Update cirros

Changes:

- https://github.com/tianon/docker-brew-cirros/commit/1f366cb: Remove i386 (unsupported upstream as of 0.6.0)
- https://github.com/tianon/docker-brew-cirros/commit/2ae8d6f: Update version-testing code for GitHub changes
- https://github.com/tianon/docker-brew-cirros/commit/d4efd05: Update README

infosiftr/stackbrew,docker-library/official-images,infosiftr/stackbrew,neo-technology/docker-official-images,docker-library/official-images,infosiftr/stackbrew,neo-technology/docker-official-images,docker-library/official-images,infosiftr/stackbrew,neo-technology/docker-official-images,neo-technology/docker-official-images,docker-library/official-images,neo-technology/docker-official-images,docker-library/official-images,neo-technology/docker-official-images,infosiftr/stackbrew,docker-library/official-images,infosiftr/stackbrew,neo-technology/docker-official-images,docker-library/official-images,docker-library/official-images,infosiftr/stackbrew,neo-technology/docker-official-images,docker-library/official-images,infosiftr/stackbrew,infosiftr/stackbrew,docker-library/official-images,neo-technology/docker-official-images,neo-technology/docker-official-images,docker-library/official-images,infosiftr/stackbrew,neo-technology/docker-official-images,infosiftr/stackbrew,neo-technology/docker-official-images,neo-technology/docker-official-images,docker-library/official-images,infosiftr/stackbrew,docker-library/official-images,infosiftr/stackbrew,docker-library/official-images,neo-technology/docker-official-images,infosiftr/stackbrew