Fix link

free-courses-en.md

@@ -99,7 +99,7 @@
 
 ### Scala
 * [Functional Programming Principles in Scala](https://www.coursera.org/course/progfun)
-* [Principles of Reactive Programming](https://class.coursera.org/reactive)
+* [Principles of Reactive Programming](https://www.coursera.org/course/reactive)
 
 
 ### Swift