[NeuralChat] Fix RAG example for retrieval plugin parameter change (#1111)

Fix RAG example for retrieval plugin parameter change Signed-off-by: lvliang-intel <liang1.lv@intel.com>

Author: lvliang-intel

intel_extension_for_transformers/neural_chat/examples/deployment/rag/askdoc.yaml

@@ -30,7 +30,7 @@ retrieval:
  enable: true
  args:
  input_path: "./askdoc_docs"
- persist_dir: "./askdoc_persist"
+ persist_directory: "./askdoc_persist"
  response_template: "We cannot find suitable content to answer your query, please contact AskGM to find help. Mail: ask.gm.zizhu@intel.com."
  append: False