ubuntu -> bionic
debian -> stretch

just run ```build.sh Dockerfile.debian``` instead

also a minor change to aptly graph in update_mirror.sh

mirroring all open source components makes the mirror more useful

the repo key wasn't in the right directory so it wasn't accessible
through nginx

the original update_mirror.sh only allowed for mirroring the main
repository. left out restricted, multiverse, etc. the component is now
an array so it is easy to add additional components if you want to mirror
more than just main