Switch to Jason for json handling.

It's twice as fast and will be the standard in the coming ecto.

mix.exs

@@ -41,6 +41,7 @@ defmodule Pleroma.Mixfile do
      {:calendar, "~> 0.16.1"},
      {:cachex, "~> 2.1"},
      {:httpoison, "~> 0.11.2"},
+     {:jason, "~> 1.0"},
      {:ex_machina, "~> 2.0", only: :test},
      {:credo, "~> 0.7", only: [:dev, :test]}]
   end