Use pseudo-var __STACKTRACE__ instead System module

Using `System.get_stacktrace()` may cause the emulator to hold on to the stack trace for a very
long time

More details in: elixir-lang/elixir#7097

Author: wevtimoteo

lib/engine_credo/cli.ex

@@ -17,7 +17,7 @@ defmodule EngineCredo.CLI do
   rescue
     error ->
       # credo:disable-for-next-line Credo.Check.Warning.IoInspect
-      IO.puts(:stderr, Exception.format(:error, error, System.stacktrace()))
+      IO.puts(:stderr, Exception.format(:error, error, __STACKTRACE__))
       System.halt(1)
   end
 end