Update agent_vectorstore.ipynb (#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!

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?\")"
    ]
   },
   {