Replace HTTPoison with Tesla for kocaptha

lib/pleroma/captcha/kocaptcha.ex

@@ -8,7 +8,7 @@ defmodule Pleroma.Captcha.Kocaptcha do
   def new() do
     endpoint = Pleroma.Config.get!([__MODULE__, :endpoint])
 
-    case HTTPoison.get(endpoint <> "/new") do
+    case Tesla.get(endpoint <> "/new") do
       {:error, _} ->
         %{error: "Kocaptcha service unavailable"}