Use 0.19 as floki dependency

mix.exs

@@ -34,7 +34,7 @@ defmodule Premailex.Mixfile do
   # Run "mix help deps" to learn about dependencies.
   defp deps do
     [
-      {:floki, "~> 0.19.2"},
+      {:floki, "~> 0.19"},
       {:httpoison, "~> 1.0"},
       {:credo, "~> 0.8", only: [:dev, :test], runtime: false},
       {:bypass, "~> 0.8", only: :test},