chore: replace deprecated function

Author: puzza007

lib/dogstatsd/statsd.ex

@@ -164,7 +164,7 @@ defmodule DogStatsd.Statsd do
           socket,
           host(dogstatsd) |> String.to_charlist(),
           port(dogstatsd),
-          message |> String.to_char_list()
+          message |> String.to_charlist()
         )
 
         :gen_udp.close(socket)

test/dogstatsd_test.exs

@@ -360,7 +360,7 @@ defmodule DogStatsdTest do
       Enum.into(1..50, [])
       |> Enum.map(fn _ -> "mycounter:1|c" end)
       |> Enum.join("\n")
-      |> String.to_char_list()
+      |> String.to_charlist()
 
     assert_receive {:udp, _port, _from_ip, _from_port, ^theoretical_reply}