Fix blank lines after Machine Learning section

Author: Anshul-Patidar

books/free-programming-books-subjects.md

@@ -415,7 +415,6 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 * [Information Retrieval: Implementing and Evaluating Search Engines](https://mitmecsept.files.wordpress.com/2018/05/stefan-bc3bcttcher-charles-l-a-clarke-gordon-v-cormack-information-retrieval-implementing-and-evaluating-search-engines-2010-mit.pdf) - Stefan Böttcher, Charles L. A. Clarke, Gordon V. Cormack (PDF)
 * [Introduction to Information Retrieval](https://nlp.stanford.edu/IR-book/information-retrieval-book.html)
 
-
 ### Licensing
 
 * [Creative Commons: a user guide](https://archive.org/download/CreativeCommonsUserGuide/CreativeCommonsUserGuide.pdf) - Simone Aliprandi (PDF)