Use Base.encode32 when generating cookie to avoid unsafe chars, closes #9328

Author: José Valim

lib/mix/lib/mix/release.ex

@@ -428,7 +428,7 @@ defmodule Mix.Release do
     end
   end
 
-  defp random_cookie, do: Base.url_encode64(:crypto.strong_rand_bytes(40))
+  defp random_cookie, do: Base.encode32(:crypto.strong_rand_bytes(32))
 
   @doc """
   Makes the start_erl.data file with the