Fix Elixir 1.19 warning

Author: fhunleth

mix.exs

@@ -20,12 +20,7 @@ defmodule NervesSystemBbb.MixProject do
       package: package(),
       deps: deps(),
       aliases: [loadconfig: [&bootstrap/1]],
-      docs: docs(),
-      preferred_cli_env: %{
-        docs: :docs,
-        "hex.build": :docs,
-        "hex.publish": :docs
-      }
+      docs: docs()
     ]
   end
 
@@ -39,6 +34,10 @@ defmodule NervesSystemBbb.MixProject do
     Mix.Task.run("loadconfig", args)
   end
 
+  def cli do
+    [preferred_envs: %{docs: :docs, "hex.build": :docs, "hex.publish": :docs}]
+  end
+
   defp nerves_package do
     [
       type: :system,