Fix deprecation error when using in 1.18 projects

Author: Kuret

lib/ex_oauth2_provider/mixin/expirable.ex

@@ -40,9 +40,10 @@ defmodule ExOauth2Provider.Mixin.Expirable do
   @spec is_expired?(Schema.t() | nil) :: boolean()
   def is_expired?(nil), do: true
   def is_expired?(%{expires_in: nil, inserted_at: _}), do: false
+
   def is_expired?(%struct{expires_in: expires_in, inserted_at: inserted_at}) do
-    now  = SchemaHelpers.__timestamp_for__(struct, :inserted_at)
-    type = now.__struct__()
+    now = SchemaHelpers.__timestamp_for__(struct, :inserted_at)
+    type = now.__struct__
 
     inserted_at
     |> type.add(expires_in, :second)