Fix blank lines between sections for linter

Author: Anshul-Patidar

books/free-programming-books-subjects.md

@@ -443,6 +443,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Elements of AI](https://www.elementsofai.com) - MinnaLearn, University of Helsinki
 * [Explorations in Parallel Distributed Processing: A Handbook of Models, Programs, and Exercises](https://web.stanford.edu/group/pdplab/pdphandbook) - James L. McClelland
 * [Fast.ai - Practical Deep Learning for Coders](https://course.fast.ai)
+
 * [Foundations of Machine Learning, Second Edition](https://mitpress.ublish.com/ebook/foundations-of-machine-learning--2-preview/7093/Cover) - Mehryar Mohri, Afshin Rostamizadeh, Ameet Talwalkar
 * [Free and Open Machine Learning](https://nocomplexity.com/documents/fossml/) - Maikel Mardjan (HTML)
 * [Gaussian Processes for Machine Learning](https://www.gaussianprocess.org/gpml/) - Carl Edward Rasmussen, Christopher K.I. Williams