wrong links in toc (#2078)

free-programming-books-de.md

@@ -5,8 +5,8 @@
 * [Android](#android)
 * [Assembly Language](#assembly-language)
 * [C](#c)
-* [C#](#c-1)
-* [C++](#c-2)
+* [C#](#c-sharp)
+* [C++](#c-1)
 * [Git](#git)
 * [Groovy](#groovy)
 * [HTML & CSS](#html--css)