Fix DateTime comparison

!420 used Date.compare/2 instead of DateTime.compare/2

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

lib/mobilizon/events/event.ex

@@ -167,7 +167,7 @@ defmodule Mobilizon.Events.Event do
     case fetch_field(changeset, :begins_on) do
       {_, begins_on} ->
         validate_change(changeset, :ends_on, fn :ends_on, ends_on ->
-          if Date.compare(begins_on, ends_on) == :gt,
+          if DateTime.compare(begins_on, ends_on) == :gt,
             do: [ends_on: "ends_on cannot be set before begins_on"],
             else: []
         end)