Mix don't fetch deps from rebar.config

I want to use erlang lib in elixir. but I found I can’t get erlang deps from mix.

mix new test
cat mix.exs

def application do
    [applications: [:logger, :observer_cli]]
  end
  defp deps do
    [{:observer_cli, "~> 1.0.8"}]
  end

mix deps.get

Result:
it only get observer_cli deps, but observer_cli has recon deps.

➜ test mix deps.tree
test
└── observer_cli ~> 1.0.8 (Hex package)
➜ test mix app.tree
test
├── elixir
├── logger
│ └── elixir
└── observer_cli
** (Mix) could not find application recon

Why mix doesn’t fetch recon from observer_cli’s rebar.config
https://github.com/zhongwencool/observer_cli/blob/master/rebar.config