Fix link to "A Guide to Python's Magic Methods"

free-programming-books.md

@@ -1524,7 +1524,7 @@ See also [TeX](#tex)
 ### Python
 * [A Beginner's Python Tutorial](http://en.wikibooks.org/wiki/A_Beginner%27s_Python_Tutorial)
 * [A Bit of Python and Other Things](https://github.com/RafeKettler/magicmethods)
-* [A Guide to Python's Magic Methods](http://www.rafekettler.com/magicmethods.html) - Rafe Kettler
+* [A Guide to Python's Magic Methods](https://github.com/RafeKettler/magicmethods) - Rafe Kettler
 * [Automate the Boring Stuff](http://automatetheboringstuff.com/chapter0/) - Al Sweigart
 * [Biopython](http://biopython.org/DIST/docs/tutorial/Tutorial.pdf)
 * [Building Skills in Object-Oriented Design (Python)](http://www.itmaybeahack.com/book/oodesign-python-2.1/latex/BuildingSkillsinOODesign.pdf) (PDF) (2.1.1)