chore(deps): update dependency phoenix_pubsub to v2

mix.exs

@@ -31,7 +31,7 @@ defmodule Eblog.Mixfile do
   # Type `mix help deps` for examples and options.
   defp deps do
     [{:phoenix, "~> 1.3.4"},
-     {:phoenix_pubsub, "~> 1.0"},
+     {:phoenix_pubsub, "== 2.0.0"},
      {:phoenix_ecto, "~> 3.0"},
      {:postgrex, ">= 0.0.0"},
      {:phoenix_html, "~> 2.6"},