Update app.py

app.py

@@ -13,7 +13,7 @@ DEFAULT_API_URL = "https://agents-course-unit4-scoring.hf.space"
 import os
 from dotenv import load_dotenv
 from langgraph.graph import START, END, StateGraph, MessagesState
-from langgraph.prebuilt import ToolNode
+
 from langchain_google_genai import ChatGoogleGenerativeAI
 from langchain_core.messages import SystemMessage, HumanMessage, AIMessage
 from langchain_core.tools import tool