Remove stacktrace warning

Author: felipesere

lib/display/failure.ex

@@ -49,7 +49,7 @@ defmodule Display.Failure do
   end
 
   defp format_error(error) do
-    trace = System.stacktrace() |> Enum.take(2)
+    trace = :erlang.get_stacktrace() |> Enum.take(2)
     Paint.red(Exception.format(:error, error, trace))
   end
 

lib/execute.ex

@@ -40,7 +40,7 @@ defmodule Execute do
 
   defp expand(error, module) do
     {file, line} =
-      System.stacktrace()
+      :erlang.get_stacktrace()
       |> Enum.drop_while(&(!in_koan?(&1, module)))
       |> List.first()
       |> extract_file_and_line