fixed a typo

app.py

@@ -10,7 +10,7 @@ sql_file = 'faiss_doc_store.db'
 faiss_file = 'faiss_index.faiss'
 
 # %% ------------------------------------------- Creating Doc store
-if not os.path.exists(sql_file) or not os.path.exits(faiss_file):
+if not os.path.exists(sql_file) or not os.path.exists(faiss_file):
     from haystack.document_stores import FAISSDocumentStore
     from haystack.nodes import DensePassageRetriever
     from haystack.utils import convert_files_to_docs, clean_wiki_text