updated module docs

lib/mix/tasks/dialyzer.ex

@@ -83,6 +83,8 @@ defmodule Mix.Tasks.Dialyzer do
 
   * `dialyzer: :plt_file` - Deprecated - specify the plt file name to create and use - default is to create one in the project's current build environmnet (e.g. _build/dev/) specific to the Erlang/Elixir version used. Note that use of this key in version 0.4 or later will produce a deprecation warning - you can silence the warning by providing a pair with key :no_warn e.g. `plt_file: {:no_warn,"filename"}`.
 
+  * `dialyzer: :plt_local_path` - specify the plt directory name to create and use - default is the project's current build environmnet (e.g. _build/dev/).
+
   * `dialyzer: :plt_core_path` - specify an alternative to MIX_HOME to use to store the Erlang and Elixir core files.
 
   * `dialyzer: :ignore_warnings` - specify file path to filter well-known warnings.