update vectorstore.ipynb (#2239)

Hello!
Maybe there's a mistake in the .ipynb, where `create_vectorstore_agent`
should be `create_vectorstore_router_agent`

Cheers!

docs/modules/agents/toolkits/examples/vectorstore.ipynb

@@ -247,7 +247,7 @@
     "    vectorstores=[vectorstore_info, ruff_vectorstore_info],\n",
     "    llm=llm\n",
     ")\n",
-    "agent_executor = create_vectorstore_agent(\n",
+    "agent_executor = create_vectorstore_router_agent(\n",
     "    llm=llm,\n",
     "    toolkit=router_toolkit,\n",
     "    verbose=True\n",