fix: only use ex_doc in dev

Author: mhanberg

mix.exs

@@ -36,7 +36,7 @@ defmodule Tableau.MixProject do
       {:plug_cowboy, "~> 2.0"},
       {:plug_static_index_html, "~> 1.0"},
       {:file_system, "~> 0.2"},
-      {:ex_doc, ">= 0.0.0"},
+      {:ex_doc, ">= 0.0.0", only: :dev},
       # {:yaml_front_matter, "~> 1.0"},
       # {:jason, "~> 1.4"},
       # {:toml, "~> 0.6.2"},