Use cli/0 in mix.exs instead of :preferred_cli_env

This resolves a warning on Elixir 1.19:

    warning: setting :preferred_cli_env in your mix.exs "def project" is deprecated, set it inside "def cli" instead:

        def cli do
          [preferred_envs: [coveralls: :test, "coveralls.html": :test, "coveralls.github": :test, docs: :dev]]
        end

Author: the-mikedavis

mix.exs

@@ -13,12 +13,6 @@ defmodule MintWebSocket.MixProject do
       start_permanent: Mix.env() == :prod,
       deps: deps(),
       test_coverage: [tool: ExCoveralls],
-      preferred_cli_env: [
-        coveralls: :test,
-        "coveralls.html": :test,
-        "coveralls.github": :test,
-        docs: :dev
-      ],
       dialyzer: [
         plt_local_path: "priv/plts",
         plt_add_apps: [:mix]
@@ -37,6 +31,17 @@ defmodule MintWebSocket.MixProject do
     ]
   end
 
+  def cli do
+    [
+      preferred_envs: [
+        coveralls: :test,
+        "coveralls.html": :test,
+        "coveralls.github": :test,
+        docs: :dev
+      ]
+    ]
+  end
+
   defp deps do
     [
       {:mint, "~> 1.4 and >= 1.4.1"},