[Bugfix] Fix small typo in the example of Streaming delimiter

[bravo325806]

fix small typo in the example of Streaming delimiter
This is apiserver delimiter

[github-actions]

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[DarkLight1337]

Can you verify that streaming still works for your PR? In case it triggers a regression from #2756

[bravo325806]

Yes, streaming still can work
The #2756 is fix server response regarding json packet boundary determination.
I just fix the client json decoding in the example,

Below is my test code

python -m vllm.entrypoints.api_server --model  /path/to/model

and send message

import requests
import json
params = {"prompt": "Hello?",
          "temperature": 0,
          "stream": "True", 
          "max_tokens": 128}
        
resp = requests.post('http://localhost:8000/generate', json=params)
for chunk in resp.iter_lines(chunk_size=8192,
                             decode_unicode=False,
                             delimiter=b"\0"):

    if chunk:
        data = json.loads(chunk.decode("utf-8"))
        output = data["text"]
        print(output)

if no change \0 to \n, you'll get an JSONDecodeError: Extra data error

[DarkLight1337]

Thanks for fixing and testing!