fix date typo (#640)

examples/evaluation/How_to_eval_abstractive_summarization.ipynb

@@ -712,7 +712,7 @@
     "- [G-EVAL: NLG Evaluation Using GPT-4 with Better Human Alignment](https://arxiv.org/pdf/2303.16634.pdf) - Liu Y, Iter D, Xu Y, Wang S, Xu R, Zhu C. Published May, 2023.\n",
     "- [BERTScore: Evaluating Text Generation with BERT](https://arxiv.org/abs/1904.09675) - Zhang T, Kishore V, Wu F, Weinberger KQ, Artzi Y. Published online February, 2020.\n",
     "- [ROUGE: A Package for Automatic Evaluation of Summaries](https://aclanthology.org/W04-1013/) - Lin CY. Published July, 2004.\n",
-    "- [SummEval: Re-evaluating Summarization Evaluation](https://aclanthology.org/2021.tacl-1.24) - Fabbri et al. Published April, 2024.\n"
+    "- [SummEval: Re-evaluating Summarization Evaluation](https://aclanthology.org/2021.tacl-1.24) - Fabbri et al. Published April, 2021.\n"
    ]
   }
  ],