Add :crypto to extra_applications to prevent warnings when running

`mix deps.compile`

mix.exs

@@ -23,7 +23,7 @@ defmodule EventBus.Mixfile do
   # Type "mix help compile.app" for more information
   def application do
     # Specify extra applications you'll use from Erlang/Elixir
-    [extra_applications: [:logger], mod: {EventBus.Application, []}]
+    [extra_applications: [:logger, :crypto], mod: {EventBus.Application, []}]
   end
 
   defp elixirc_paths(:test) do