Enable observer in dev (#564)

Author: Madumo

mix.exs

@@ -24,13 +24,16 @@ defmodule ElixirBoilerplate.Mixfile do
   def application do
     [
       mod: {ElixirBoilerplate.Application, []},
-      extra_applications: [:logger, :runtime_tools]
+      extra_applications: extra_applications(Mix.env()) ++ [:logger, :runtime_tools]
     ]
   end
 
   defp elixirc_paths(:test), do: ["lib", "test/support"]
   defp elixirc_paths(_), do: ["lib"]
 
+  defp extra_applications(:dev), do: [:observer, :wx]
+  defp extra_applications(_), do: []
+
   defp aliases do
     [
       "assets.deploy": [