Update Swift version badge to 6.1

Author: jihoonahn

README.md

@@ -1,7 +1,7 @@
 # Swift NetworkKit
 
 ![Official](https://badge.pelagornis.com/official.svg)
-[![Swift](https://img.shields.io/badge/Swift-6.0-orange.svg)](https://swift.org)
+[![Swift](https://img.shields.io/badge/Swift-6.1-orange.svg)](https://swift.org)
 [![Platform](https://img.shields.io/badge/Platform-iOS%20%7C%20macOS%20%7C%20tvOS%20%7C%20visionOS%20%7C%20watchOS-lightgrey.svg)](https://developer.apple.com)
 [![License](https://img.shields.io/badge/License-MIT-blue.svg)](LICENSE)