Fix a typo for the author's name in Simplification (sebastianruder#550)

The author's last name is Zhu instead of Zu as shown in the link http://aclweb.org/anthology/C10-1152.

english/simplification.md

@@ -46,7 +46,7 @@ Since a simplification could involve text transformations beyond paraphrasing (w
 
 #### PWKP / WikiSmall
 
-[Zu et al. (2010)](http://aclweb.org/anthology/C10-1152) compiled a parallel corpus with more than 108K sentence pairs from 65,133 Wikipedia articles, allowing **1-to-1 and 1-to-N alignments**. The latter type of alignments represents instances of sentence splitting. The original full corpus can be found [here](https://www.informatik.tu-darmstadt.de/ukp/research_6/data/sentence_simplification/simple_complex_sentence_pairs/index.en.jsp). The test set is composed of 100 instances, with **one simplification reference per original sentence**. [Zhang and Lapata (2017)](http://aclweb.org/anthology/D17-1062) released a more standardised split of this dataset called [*WikiSmall*](https://github.com/XingxingZhang/dress), with 89,042 instances for training, 205 for development and the same original 100 instances for testing. 
+[Zhu et al. (2010)](http://aclweb.org/anthology/C10-1152) compiled a parallel corpus with more than 108K sentence pairs from 65,133 Wikipedia articles, allowing **1-to-1 and 1-to-N alignments**. The latter type of alignments represents instances of sentence splitting. The original full corpus can be found [here](https://www.informatik.tu-darmstadt.de/ukp/research_6/data/sentence_simplification/simple_complex_sentence_pairs/index.en.jsp). The test set is composed of 100 instances, with **one simplification reference per original sentence**. [Zhang and Lapata (2017)](http://aclweb.org/anthology/D17-1062) released a more standardised split of this dataset called [*WikiSmall*](https://github.com/XingxingZhang/dress), with 89,042 instances for training, 205 for development and the same original 100 instances for testing. 
 
 We present the models tested in this dataset **ranked by BLEU score** (or SARI if BLEU is not available). SARI cannot be reliably computed in this dataset since it does not contain multiple simplification references per original sentence. In addition, there are instances of more advanced simplification transformations (e.g. splitting) which SARI does not assess by definition.