ruby

Docker storage engines remember all the layers by storing incremental differences so it makes little sense to have a layer that only removes things (like the last RUN in https://github.com/iron-io/dockers/blob/master/ruby/Dockerfi...). You can see with `docker history <image>` that this layer has 0 bytes and you can access anything that it removes by using the parent image (`docker run -it 88ae7e32865f ls /var/cache/apk`). In this case it doesn't make much difference (a couple of MB perhaps) but often you'll see people chaining all the commands and ending it with a cleanup in a single RUN like here: https://github.com/docker-library/ruby/blob/ccbf9e54f60ba245...