I tried end_sequence and indeed works, I would suggest updating the doc, thanks in any case! 
    data = json.dumps(
        {
            "inputs": "1+1=2\n2+2=",
            "parameters": {
                "max_length": 50,
                "num_return_sequences": 1,
                "return_text": False,
                "return_full_text": False,
                "do_sample": True,
                "top_k": 50,
                "top_p": 0.95,
                "end_sequence": "\n"
            },
            "options": {
                "wait_for_model": True,
            },
        }
    )