chore(deps): update dependency cowboy to v2

mix.exs

@@ -37,7 +37,7 @@ defmodule Eblog.Mixfile do
      {:phoenix_html, "~> 2.6"},
      {:phoenix_live_reload, "~> 1.0", only: :dev},
      {:gettext, "~> 0.11"},
-     {:cowboy, "~> 1.0"}]
+     {:cowboy, "== 2.8.0"}]
   end
 
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