Set ex_doc dependency to >= 0.40.0

Author: FelonEkonom

mix.exs

@@ -61,7 +61,7 @@ defmodule Membrane.WebRTC.Plugin.Mixfile do
       {:membrane_file_plugin, "~> 0.17.0", only: :test},
       {:membrane_realtimer_plugin, "~> 0.10.0", only: :test},
       {:membrane_opus_plugin, "~> 0.20.0", only: :test},
-      {:ex_doc, "~> 0.40", only: :dev, runtime: false},
+      {:ex_doc, ">= 0.40.0", only: :dev, runtime: false},
       {:dialyxir, ">= 0.0.0", only: :dev, runtime: false},
       {:credo, ">= 0.0.0", only: :dev, runtime: false}
     ]