Update README.md

Author: floriankugler

README.md

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-# Functional Programming in Swift
+# Functional Swift by [objc.io](https://www.objc.io)
 
-This repository is used as issue tracker for the [Functional Programming in Swift book](http://www.objc.io/books). Please file an issue here for any kind of feedback!
+This repository is used as issue tracker for the [Functional Swift book](https://www.objc.io/books/fpinswift). Please file an issue here for any kind of feedback!