Merge branch 'pr/1976'

free-programming-books.md

@@ -497,7 +497,8 @@
 * [Coursera](https://www.coursera.org)
 * [edX](https://www.edx.org)
 * [FutureLearn](https://www.futurelearn.com)
-* [MIT OCW](http://ocw.mit.edu/index.htm)
+* [MIT OCW](http://ocw.mit.edu)
+* [openHPI](https://open.hpi.de)
 * [Platzi](https://courses.platzi.com)
 * [Udacity](https://www.udacity.com)