Updating Nomad + Frodo deps
Adding `NOMAD_ENV=prod` to Procfile to ensure that Nomad uses the 'prod' environment config
Fixing the Nomad config file

We now have two 'environments' - the default config in the root of the
map, and the production config. We switch between these with the
NOMAD_ENV environment variable - setting this to "prod" will activate
the production config.

Normally, Nomad (and, by extension, Frodo) will use the default config
provided (i.e. port 3000, 'cljs-repl?' true etc), but if we switch it to
prod, it'll look in the PORT env-var for the port, and turn the
cljs-repl off.
This isn't a main fn, renaming it to 'make-handler'

Frodo handles the -main function for you, no need to worry about
declaring one or specifying it in project.clj