replace coherence with guardian

lib/eventos_web/auth_error_handler.ex

@@ -0,0 +1,8 @@
+defmodule EventosWeb.AuthErrorHandler do
+  import Plug.Conn
+
+  def auth_error(conn, {type, _reason}, _opts) do
+    body = Poison.encode!(%{message: to_string(type)})
+    send_resp(conn, 401, body)
+  end
+end