Standize C++ Headings (#5275)

courses/free-courses-en.md

@@ -8,7 +8,7 @@
 * [Bootstrap](#bootstrap)
 * [C](#c)
 * [C#](#c-sharp)
-* [C++](#c-1)
+* [C++](#cpp)
 * [Clojure](#clojure)
 * [Compilers](#compilers)
 * [CUDA](#cuda)
@@ -168,7 +168,7 @@
 * [Learn how to program: C#](https://www.learnhowtoprogram.com/c) - Epicodus Inc.
 
 
-### C++
+<h3 id="cpp">C++</h3>
 
 * [C++ For Programmers](https://www.udacity.com/course/c-for-programmers--ud210) - Catherine Gamboa (Udacity)
 * [C++ Programming Tutorial for Beginners (For Absolute Beginners)](https://www.youtube.com/playlist?list=PLS1QulWo1RIYSyC6w2-rDssprPrEsgtVK) - ProgrammingKnowledge