mix: add ex_aws and ex_aws_s3 dependencies

mix.exs

@@ -46,6 +46,8 @@ defmodule Pleroma.Mixfile do
       {:httpoison, "~> 1.2.0"},
       {:jason, "~> 1.0"},
       {:mogrify, "~> 0.6.1"},
+      {:ex_aws, "~> 2.0"},
+      {:ex_aws_s3, "~> 2.0"},
       {:ex_machina, "~> 2.2", only: :test},
       {:credo, "~> 0.9.3", only: [:dev, :test]},
       {:mock, "~> 0.3.1", only: :test}