Fix EbookFoundation#6638 (EbookFoundation#6640)

* Resolved EbookFoundation#6638

* Added author

Author: LuigiImVector

books/free-programming-books-subjects.md

@@ -360,7 +360,7 @@ Books that cover a specific programming language can be found in the  [BY PROGRA
 * [The Elements of Statistical Learning](https://web.stanford.edu/~hastie/ElemStatLearn/) - Trevor Hastie, Robert Tibshirani, and Jerome Friedman
 * [The LION Way: Machine Learning plus Intelligent Optimization](https://intelligent-optimization.org/LIONbook/lionbook_3v0.pdf) - Roberto Battiti, Mauro Brunato (PDF)
 * [The Mechanics of Machine Learning](https://mlbook.explained.ai) - Terence Parr and Jeremy Howard
-* [The Python Game Book](http://thepythongamebook.com/en%3Astart)
+* [The Python Game Book](https://web.archive.org/web/20210308080726/https://thepythongamebook.com/en%3Astart) - Horst Jens *(:card_file_box: archived)*
 * [Top 10 Machine Learning Algorithms Every Engineer Should Know](https://www.dezyre.com/article/top-10-machine-learning-algorithms/202) - Binny Mathews and Omair Aasim
 * [Understanding Machine Learning: From Theory to Algorithms](https://www.cs.huji.ac.il/~shais/UnderstandingMachineLearning) - Shai Shalev-Shwartz, Shai Ben-David