Update broken link to google's cpp style guide

free-programming-books.md

@@ -842,7 +842,7 @@
 * [CS106X Programming Abstractions in C++](http://web.stanford.edu/class/cs106x/)
 * [Financial Numerical Recipes in C++](http://finance.bi.no/~bernt/gcc_prog/recipes/) - Bernt Arne Ødegaard
 * [Game Programming Patterns](http://gameprogrammingpatterns.com)
-* [Google's C++ Style Guide](http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml)
+* [Google's C++ Style Guide](https://google.github.io/styleguide/cppguide.html)
 * [How To Think Like a Computer Scientist: C++ Version](http://greenteapress.com/thinkcpp/index.html) - Allen B. Downey
 * [Introduction to Design Patterns in C++ with Qt](http://ptgmedia.pearsoncmg.com/images/9780131879058/downloads/0131879057_Ezust_book.pdf) (PDF)
 * [Joint Strike Fighter, C++ Coding Standards, by Bjarne Stroustrup](http://www.stroustrup.com/JSF-AV-rules.pdf) (PDF)