module :unicode_util not available Phoenix/elixir

Question

I was trying the Ueberauth library for GitHub login. In the login function, I'm getting an error saying that

"function :unicode_util.lowercase/1 is undefined (module :unicode_util is not available)"

The code that I've used

defmodule Discuss.AuthController do
  use Discuss.Web, :controller
  plug Ueberauth

  def callback(conn, params) do
    IO.inspect "++++++++++"
    IO.inspect(conn.assigns)
    IO.inspect "++++++++++"
    IO.inspect(conn.params)
    IO.inspect "++++++++++"
  end
end