Add missing @doc since (#11443)

Author: wojtekmach

lib/elixir/lib/enum.ex

@@ -2578,6 +2578,7 @@ defmodule Enum do
       [:a, :b, :c, :e, :f, :g, :d]
 
   """
+  @doc since: "1.13.0"
   def slide(enumerable, range_or_single_index, insertion_index)
 
   def slide(enumerable, single_index, insertion_index) when is_integer(single_index) do

lib/mix/lib/mix/tasks/format.ex

@@ -213,6 +213,7 @@ defmodule Mix.Tasks.Format do
   to be formatted. The options are returned for reflection
   purposes.
   """
+  @doc since: "1.13.0"
   def formatter_for_file(file, opts \\ []) do
     {dot_formatter, formatter_opts} = eval_dot_formatter(opts)