Updated defexception docs

Author: jwarwick

lib/elixir/lib/kernel.ex

@@ -1505,8 +1505,8 @@ defmodule Kernel do
  @doc """
  Defines an exception.
 
- Exceptions are simply records and therefore `defexception/4` has
- the same API and similar behavior to `defrecord/4` with two notable
+ Exceptions are simply records and therefore `defexception/3` has
+ the same API and similar behavior to `defrecord/3` with two notable
  differences:
 
  1) Unlike records, exceptions are documented by default;