Migrate to comeonin 4 and Cachex 3

Also fix some warning in the code and add a missing alias

mix.exs

@@ -36,12 +36,13 @@ defmodule Pleroma.Mixfile do
       {:postgrex, ">= 0.0.0"},
       {:gettext, "~> 0.11"},
       {:cowboy, "~> 1.0", override: true},
-      {:comeonin, "~> 3.0"},
+      {:comeonin, "~> 4.0"},
+      {:pbkdf2_elixir, "~> 0.12"},
       {:trailing_format_plug, "~> 0.0.5"},
       {:html_sanitize_ex, "~> 1.3.0-rc1"},
       {:phoenix_html, "~> 2.10"},
       {:calendar, "~> 0.16.1"},
-      {:cachex, "~> 2.1"},
+      {:cachex, "~> 3.0"},
       {:httpoison, "~> 1.1.0"},
       {:jason, "~> 1.0"},
       {:ex_machina, "~> 2.0", only: :test},