installer: use preferred_envs instead of preferred_cli_env

Author: SteffenDE

installer/mix.exs

@@ -37,7 +37,6 @@ defmodule Phx.New.MixProject do
         links: %{"GitHub" => @scm_url},
         files: ~w(lib templates mix.exs README.md)
       ],
-      preferred_cli_env: [docs: :docs],
       source_url: @scm_url,
       docs: docs(),
       homepage_url: "https://www.phoenixframework.org",
@@ -50,6 +49,10 @@ defmodule Phx.New.MixProject do
     ]
   end
 
+  def cli do
+    [preferred_envs: [docs: :docs]]
+  end
+
   def application do
     [
       extra_applications: [:eex, :crypto]