mix failing on heroku

mix.exs

defmodule ChatExperiment.Mixfile do
  use Mix.Project

  def project do
    [ app: :chat_experiment,
      version: "0.0.1",
      elixir: "~> 0.12.0",
      deps: deps ]
  end

  # Configuration for the OTP application
  def application do
    [ mod: {ChatExperiment, []},
      applications: [:cowboy]]
  end

  # Returns the list of dependencies in the format:
  # { :foobar, git: "https://github.com/elixir-lang/foobar.git", tag: "0.1" }
  #
  # To specify particular versions, regardless of the tag, do:
  # { :barbat, "~> 0.1", github: "elixir-lang/barbat" }
  defp deps do
    [
      {:cowboy, "0.9.0",[github: "extend/cowboy", tag: "0.9.0"]},
      {:json, [github: "cblage/elixir-json"]}
    ]
  end
end

output

2013-12-23T17:04:26.600506+00:00 heroku[web.1]: State changed from crashed to starting
2013-12-23T17:04:31.164654+00:00 heroku[web.1]: Starting process with command `mix run --no-halt`
2013-12-23T17:04:32.891494+00:00 app[web.1]: Unchecked dependencies for environment prod:
2013-12-23T17:04:32.891685+00:00 app[web.1]:   could not find an app file at _build/shared/lib/ranch/ebin/ranch.app, this may happen when you specified the wrong application name in your deps or if the dependency did not compile (which can be amended with `mix deps.compile`)
2013-12-23T17:04:32.891494+00:00 app[web.1]: * ranch (git://github.com/extend/ranch.git)
2013-12-23T17:04:32.892027+00:00 app[web.1]:   could not find an app file at _build/shared/lib/cowlib/ebin/cowlib.app, this may happen when you specified the wrong application name in your deps or if the dependency did not compile (which can be amended with `mix deps.compile`)
2013-12-23T17:04:32.892109+00:00 app[web.1]: * cowboy (git://github.com/extend/cowboy.git)
2013-12-23T17:04:32.891732+00:00 app[web.1]: * cowlib (git://github.com/extend/cowlib.git)
2013-12-23T17:04:32.892442+00:00 app[web.1]:   could not find an app file at _build/shared/lib/cowboy/ebin/cowboy.app, this may happen when you specified the wrong application name in your deps or if the dependency did not compile (which can be amended with `mix deps.compile`)
2013-12-23T17:04:32.900642+00:00 app[web.1]: ** (Mix) Can't continue due to errors on dependencies
2013-12-23T17:04:34.115659+00:00 heroku[web.1]: Process exited with status 1
2013-12-23T17:04:34.130013+00:00 heroku[web.1]: State changed from starting to crashed