Patch version to fix botched release

The hex script didn't complete successfully, and I managed to exclude
the version bump from the v2.0.0 release.

mix.exs

@@ -11,7 +11,7 @@ defmodule Mudbrick.MixProject do
       elixir: "~> 1.17",
       package: package(),
       start_permanent: Mix.env() == :prod,
-      version: "0.2.0",
+      version: "0.2.1",
 
       # Docs
       source_url: @scm_url,