Typo fix for Kernel.in/2 documentation. (#12010)

Author: creature

lib/elixir/lib/kernel.ex

@@ -4255,7 +4255,7 @@ defmodule Kernel do
 
       when x === 1 or x === 2 or x === 3
 
-  However, this construct will be inneficient for large lists. In such cases, it
+  However, this construct will be inefficient for large lists. In such cases, it
   is best to stop using guards and use a more appropriate data structure, such
   as `MapSet`.