fix validation universal dividend

lib/block/validation/local/universal_dividend.ex

@@ -3,6 +3,6 @@ defmodule Block.Validation.Local.UniversalDividend do
   https://git.duniter.org/documents/rfcs/-/blob/master/rfc/0010_Duniter_Blockchain_Protocol_V12.md#universal-dividend
   """
   def valid(block) do
-    block["number"] === 0 and block["dividend"] === nil
+    if block["number"] === 0, do: block["dividend"] === nil, else: true
   end
 end