Fix more deprecation warnings

Author: iamvery

lib/display/failure.ex

@@ -50,7 +50,7 @@ defmodule Display.Failure do
   end
 
   defp format_error(error) do
-    trace = System.stacktrace() |> Enum.take(2)
+    trace = Process.info(self(), :current_stacktrace) |> Enum.take(2)
     Paint.red(Exception.format(:error, error, trace))
   end
 

lib/elixir_koans.ex

@@ -3,13 +3,11 @@ defmodule ElixirKoans do
   use Application
 
   def start(_type, _args) do
-    import Supervisor.Spec
-
     children = [
-      worker(Display, []),
-      worker(Tracker, []),
-      worker(Runner, []),
-      worker(Watcher, [])
+      %{id: Display, start: {Display, :start_link, []}},
+      %{id: Tracker, start: {Tracker, :start_link, []}},
+      %{id: Runner, start: {Runner, :start_link, []}},
+      %{id: Watcher, start: {Watcher, :start_link, []}}
     ]
 
     opts = [strategy: :one_for_one, name: ElixirKoans.Supervisor]

test/executor_test.exs

@@ -7,7 +7,7 @@ defmodule ExecuteTest do
 
   test "stops at the first failing koan" do
     {:failed, %{file: file, line: line}, SampleKoan, _name} = Execute.run_module(SampleKoan)
-    assert file == 'test/support/sample_koan.ex'
+    assert file == ~c'test/support/sample_koan.ex'
     assert line == 9
   end