Merge pull request AFNetworking#4286 from rob2468/master

update README.md, the old "Foundation URL Loading System" link is 404

README.md

@@ -9,7 +9,7 @@
 [![Platform](https://img.shields.io/cocoapods/p/AFNetworking.svg?style=flat)](http://cocoadocs.org/docsets/AFNetworking)
 [![Twitter](https://img.shields.io/badge/twitter-@AFNetworking-blue.svg?style=flat)](http://twitter.com/AFNetworking)
 
-AFNetworking is a delightful networking library for iOS, macOS, watchOS, and tvOS. It's built on top of the [Foundation URL Loading System](http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/URLLoadingSystem/URLLoadingSystem.html), extending the powerful high-level networking abstractions built into Cocoa. It has a modular architecture with well-designed, feature-rich APIs that are a joy to use.
+AFNetworking is a delightful networking library for iOS, macOS, watchOS, and tvOS. It's built on top of the [Foundation URL Loading System](https://developer.apple.com/documentation/foundation/url_loading_system), extending the powerful high-level networking abstractions built into Cocoa. It has a modular architecture with well-designed, feature-rich APIs that are a joy to use.
 
 Perhaps the most important feature of all, however, is the amazing community of developers who use and contribute to AFNetworking every day. AFNetworking powers some of the most popular and critically-acclaimed apps on the iPhone, iPad, and Mac.