dockerfile: upgrade to `sameersbn/ubuntu:14.04.20150604`
dockerfile: upgrade to `sameersbn/ubuntu:14.04.20150604`

korczis/docker-squid-rubygems-proxy,boliu83/docker-squid,sameersbn/docker-squid,zultron/docker-provisioning,opendoor-labs/docker-squid-s3,Optibus/docker-squid,maqsoodumt/docker-squid,korczis/docker-squid-rubygems-proxy,linearregression/docker-squid-s3