Set ex_doc dependency to >= 0.40.0

Author: FelonEkonom

mix.exs

@@ -46,7 +46,7 @@ defmodule Membrane.Opus.Plugin.Mixfile do
       {:bundlex, "~> 1.2"},
       {:membrane_precompiled_dependency_provider, "~> 0.2.0"},
       {:dialyxir, ">= 0.0.0", only: :dev, runtime: false},
-      {:ex_doc, "~> 0.40", only: :dev, runtime: false},
+      {:ex_doc, ">= 0.40.0", only: :dev, runtime: false},
       {:credo, ">= 0.0.0", only: :dev, runtime: false},
       {:membrane_file_plugin, "~> 0.16.0", only: :test},
       {:membrane_raw_audio_parser_plugin, "~> 0.4.0", only: :test}