Fix blank lines after Machine Learning section

Author: Anshul-Patidar

books/free-programming-books-subjects.md

@@ -421,7 +421,6 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Creative Commons: a user guide](https://archive.org/download/CreativeCommonsUserGuide/CreativeCommonsUserGuide.pdf) - Simone Aliprandi (PDF)
 * [The Public Domain: Enclosing the Commons of the Mind](https://www.thepublicdomain.org/download/) - James Boyle
 
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 ### Machine Learning
 
 * [A Brief Introduction to Machine Learning for Engineers](https://arxiv.org/pdf/1709.02840.pdf) - Osvaldo Simeone (PDF)
@@ -483,7 +482,6 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Understanding Machine Learning: From Theory to Algorithms](https://www.cs.huji.ac.il/~shais/UnderstandingMachineLearning) - Shai Shalev-Shwartz, Shai Ben-David
 * [User Guide - scikit-learn](https://scikit-learn.org/stable/user_guide.html) - Scikit-learn developers (HTML) 
 
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 ### Mathematics
 
 * [A Computational Logic (1979)](https://www.cs.utexas.edu/users/boyer/acl.pdf) - Robert S. Boyer, J Strother Moore (PDF)