fix typo

examples/rag/langgraph_agentic_rag.ipynb

@@ -19,7 +19,7 @@
     "\n",
     "[Retrieval Agents](https://python.langchain.com/docs/use_cases/question_answering/conversational_retrieval_agents) are useful when we want to make decisions about whether to retrieve from an index.\n",
     "\n",
-    "To implement a retrieval agent, we simple need to give an LLM access to a retrier tool.\n",
+    "To implement a retrieval agent, we simple need to give an LLM access to a retriever tool.\n",
     "\n",
     "We can incorperate this into [LangGraph](https://python.langchain.com/docs/langgraph).\n",
     "\n",