Update Swift badge

Author: bradhowes

README.md

@@ -1,5 +1,5 @@
 [![CI](https://github.com/bradhowes/AUv3Template/actions/workflows/CI.yml/badge.svg?branch=main)](https://github.com/bradhowes/AUv3Template/actions/workflows/CI.yml)
-[![Swift 5.5](https://img.shields.io/badge/Swift-5.5-orange.svg?style=flat)](https://swift.org)
+[![Swift 6](https://img.shields.io/badge/Swift-6-orange.svg?style=flat)](https://swift.org)
 [![AUv3](https://img.shields.io/badge/AudioUnit-AUv3-orange.svg)](https://developer.apple.com/documentation/audiounit)
 [![License: MIT](https://img.shields.io/badge/License-MIT-A31F34.svg)](https://opensource.org/licenses/MIT)