Added 100 days of swift course (#3894)

free-courses-en.md

@@ -437,6 +437,7 @@
 
 ### Swift
 
+* [100 days of Swift](https://www.hackingwithswift.com/100) - Hacking With Swift
 * [How To Make An App For Beginners (iOS/Swift - 2019)](https://www.udemy.com/how-to-make-an-app-for-beginners-iosswift-2019/) - Chris Ching (Udemy)
 * [Swiftris - Build an iOS Tetris app from scratch](https://www.bloc.io/swiftris-build-your-first-ios-game-with-swift)