🔥 Fix dvm install experimental to support edge releases

[carolynvs]

Docker has stopped publishing experimental builds to a static location. Now they publish "edge" builds to https://download.docker.com/linux/static/edge/x86_64/, under named releases.

The edge builds are only vaild for a month, and older edge releases will not match the eventual stable release under the same name. So we only care about the latest edge release.

I'm thinking that we should drop "experimental" now that Docker is calling it "edge", something like:

dvm install edge

That will list the edge versions available and install the highest one.

[carolynvs]

Edge releases no longer have checksums.