Update app.py

app.py

@@ -11,6 +11,7 @@ from langchain.embeddings.openai import OpenAIEmbeddings
 from langchain.vectorstores import Chroma
 from langchain.text_splitter import TokenTextSplitter
 #from langchain.llms import OpenAI
+from langchain import OpenAI, VectorDBQA
 from langchain.chat_models import ChatOpenAI
 from langchain.chains import ChatVectorDBChain
 from langchain.chains import RetrievalQA