Feasability to use commit hash strings when determining upgrade eligability

[davidski]

While tracking changes to the nifty gganimate package, I've been wondering if it would be possible for dtupdate to compare the latest commit hash on a git repo for determining whether a package is out of date. Getting the hash from GH is simple enough, but I don't know of any mechanism for knowing what hash is associated with a devtools::github_install. Is there an existing dtupdate solution for tracking such bleeding edge code?