Update base.ex

Clean up doc

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: arcz

lib/elixir/lib/base.ex

@@ -256,8 +256,6 @@ defmodule Base do
   @doc """
   Decodes a base 64 encoded string into a binary string.
 
-  The following alphabet is used both for encoding and decoding:
-
   An `ArgumentError` exception is raised if the padding is incorrect or
   a non-alphabet character is present in the string.