Unable to Install Darwin if Frog is Already Installed

[dented42]

It looks like this might be a regression of issue #5, but installing Darwin on a system that already has frog gives me the following output:

Resolving "darwin" via https://download.racket-lang.org/releases/8.12/catalog/
Resolving "darwin" via https://pkgs.racket-lang.org
Using cached17128692271712869227731 for https://github.com/pmatos/darwin.git
raco pkg install: packages conflict
  package: darwin
  package: frog
  module path: (lib "example/_src/posts/2013-06-19-a-scribble-post.scrbl")