Update app.py

switching to gpt-3.5-turbo

app.py

@@ -62,7 +62,7 @@ async def init():
     docsearch = await cl.make_async(FAISS.from_documents)(documents, embedder)
 
     chain = RetrievalQA.from_chain_type(
-        ChatOpenAI(model="gpt-4", temperature=0, streaming=True),
+        ChatOpenAI(model="gpt-3.5-turbo", temperature=0, streaming=True),
         chain_type="stuff",
         return_source_documents=True,
         retriever=docsearch.as_retriever(),