Fix Quartz port not being passed correctly

When CLI options --port/--ws-port were not provided, nil values were
being explicitly passed to Server.start_link, which caused Keyword.get
to return nil instead of the default. Now we only include port options
in the keyword list if they have actual values.

lib/org_garden/cli.ex

@@ -75,13 +75,16 @@ defmodule OrgGarden.CLI do
 
     IO.puts("==> Starting development server...")
 
-    case OrgGarden.Server.start_link(
+    server_opts =
+      [
         notes_dir: notes_dir,
         output_dir: output_dir,
-           content_dir: content_dir,
-           port: opts[:port],
-           ws_port: opts[:ws_port]
-         ) do
+        content_dir: content_dir
+      ]
+      |> maybe_put(:port, opts[:port])
+      |> maybe_put(:ws_port, opts[:ws_port])
+
+    case OrgGarden.Server.start_link(server_opts) do
       {:ok, pid} ->
         IO.puts("==> Server running at http://localhost:#{opts[:port] || Config.get(:http_port, 8080)}")
         IO.puts("==> Watching #{notes_dir} for changes (Ctrl+C to stop)")
@@ -379,4 +382,7 @@ defmodule OrgGarden.CLI do
     IO.puts(:stderr, message)
     System.halt(1)
   end
+
+  defp maybe_put(keyword, _key, nil), do: keyword
+  defp maybe_put(keyword, key, value), do: Keyword.put(keyword, key, value)
 end