[FIX] remove redundant period

docs/References.rst

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 References
 ==========
 
-Zhi-Hua Zhou. `Abductive learning: Towards bridging machine learning and logical reasoning. <http://scis.scichina.com/en/2019/076101.pdf>`_. **Science China Information Sciences**, 2019, 62: 076101.
+Zhi-Hua Zhou. `Abductive learning: Towards bridging machine learning and logical reasoning <http://scis.scichina.com/en/2019/076101.pdf>`_. **Science China Information Sciences**, 2019, 62: 076101.
 
 Zhi-Hua Zhou and Yu-Xuan Huang. `Abductive learning <https://www.lamda.nju.edu.cn/publication/chap_ABL.pdf>`_. In P. Hitzler and M. K. Sarker eds., **Neuro-Symbolic Artificial Intelligence: The State of the Art**, IOP Press, Amsterdam, 2022, p.353-379