Update app.py

app.py

@@ -11,6 +11,7 @@ from llama_index.embeddings.huggingface import HuggingFaceEmbedding
 from llama_index.vector_stores.elasticsearch import ElasticsearchStore
 from llama_index.core.query_engine import CitationQueryEngine
 from llama_index.core import VectorStoreIndex
+from llama_index.core.postprocessor import SimilarityPostprocessor
 
 import torch
 from transformers import AutoTokenizer