Update agent_vectorstore.ipynb (langchain-ai#1318)

nitpicking but just thought i'd add this typo which I found when going through the How-to 😄 (unless it was intentional) also, it's amazing that you added ReAct to LangChain!

Author: akshayvkt

docs/modules/agents/examples/agent_vectorstore.ipynb

@@ -336,7 +336,7 @@
  }
  ],
  "source": [
- "agent.run(\"What did biden say about ketanji brown jackson is the state of the union address?\")"
+ "agent.run(\"What did biden say about ketanji brown jackson in the state of the union address?\")"
  ]
  },
  {