Update Dockerfile to install siphon
Update Dockerfile to install siphon

nanobox-io/nanobox-docker-build,nanobox-io/nanobox-docker-build,nanobox-io/nanobox-docker-build,pagodabox/nanobox-docker-build,nanobox-io/nanobox-docker-build,pagodabox/nanobox-docker-build