chore(deps): update dependency phoenix_pubsub to v2

Author: renovate[bot]

mix.exs

@@ -31,7 +31,7 @@ defmodule Eblog.Mixfile do
   # Type `mix help deps` for examples and options.
   defp deps do
     [{:phoenix, "== 1.6.10"},
-     {:phoenix_pubsub, "== 1.1.2"},
+     {:phoenix_pubsub, "== 2.1.3"},
      {:phoenix_ecto, "== 3.6.0"},
      {:postgrex, "== 0.16.3"},
      {:phoenix_html, "== 2.14.3"},