Support automatic dependency update checking #96

I just added support for automatic dependency update checking via Depot.

To do so I added Depot to my bin/app project's deps.edn file. Additionally, I added a new script in bin named 'outdated' using the 'clojure' execution line suggested by the Depot docs.

There are two things that would be nice to have:

1. Integrate this into Edge (i.e., Add an :outdated alias to 'bin/app' generated deps.edn, and add a 'bin/outdated' script.
2. Create and maintain some sort of Maven/Clojars/etc. artifact that tracked Edge's current version so that Depot would report that a new Edge version is available.