Add Advanced Android with Kotlin course link (#5685)

courses/free-courses-en.md

@@ -508,6 +508,7 @@
 
 ### Kotlin
 
+* [Advanced Android with Kotlin](https://www.udacity.com/course/advanced-android-with-kotlin--ud940) (Udacity)
 * [Android Kotlin Tutorial: Create Android Apps using Kotlin](https://www.youtube.com/playlist?list=PLlxmoA0rQ-Lw5k_QCqVl3rsoJOnb_00UV) - Sriyank Siddhartha (YouTube)
 * [Developing Android Apps with Kotlin](https://www.udacity.com/course/developing-android-apps-with-kotlin--ud9012) (Udacity)
 * [Kotlin Bootcamp for Programmers](https://www.udacity.com/course/kotlin-bootcamp-for-programmers--ud9011) - Aleks Haecky, Asser Samak, Sean McQuillan (Udacity)