Fix Dockerfile
Fix Dockerfile

At least now, files are now .tgz (including 1.6.2 that is the default).
Otherwise, an image is downloaded that is shown on 404 as the requested file
does not exist.

Also, the layout on the tgz has changed, so it is adapted from the new layout.

matt-deboer/docker-gc,Financial-Times/docker-gc,spotify/docker-gc