Downgrade version to 0.0.6

Accidentally skip the 0.0.6 version in the previous commit. Since the
package was not deployed to hex.pm, reverting it here to keep the
package history intact.

mix.exs

@@ -1,7 +1,7 @@
 defmodule Authzed.MixProject do
   use Mix.Project
 
-  @version "0.0.7"
+  @version "0.0.6"
   @repo_url "https://github.com/goodhamgupta/authzed_ex/"
 
   def project do