Fix some typespecs

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon/events/event.ex

@@ -43,10 +43,10 @@ defmodule Mobilizon.Events.Event do
           description: String.t(),
           ends_on: DateTime.t(),
           title: String.t(),
-          status: EventStatus.t(),
+          status: atom(),
           draft: boolean,
-          visibility: EventVisibility.t(),
-          join_options: JoinOptions.t(),
+          visibility: atom(),
+          join_options: atom(),
           publish_at: DateTime.t() | nil,
           uuid: Ecto.UUID.t(),
           online_address: String.t() | nil,