Fix accidental commented code

Author: ericmj

lib/elixir/lib/keyword.ex

@@ -36,7 +36,7 @@ defmodule Keyword do
   """
   @spec from_enum(Enum.t) :: t
   def from_enum(enum) do
-    # IO.write :stderr, "Keyword.from_enum/1 is deprecated, please use Enum.into/2 instead\n#{Exception.format_stacktrace}"
+    IO.write :stderr, "Keyword.from_enum/1 is deprecated, please use Enum.into/2 instead\n#{Exception.format_stacktrace}"
     Enum.to_list(enum)
   end