docs: update Kotlin badge

Author: lppedd

README.md

@@ -5,7 +5,7 @@
 [![License](https://img.shields.io/github/license/petertrr/kotlin-multiplatform-diff)](https://github.com/petertrr/kotlin-multiplatform-diff/blob/main/LICENSE)
 [![Maven Central](https://img.shields.io/maven-central/v/io.github.petertrr/kotlin-multiplatform-diff)](https://mvnrepository.com/artifact/io.github.petertrr)
 [![Awesome Kotlin Badge](https://kotlin.link/awesome-kotlin.svg)](https://github.com/KotlinBy/awesome-kotlin)
-[![Kotlin](https://img.shields.io/badge/kotlin-2.1.20-blue.svg?logo=kotlin)](http://kotlinlang.org)
+[![Kotlin](https://img.shields.io/badge/kotlin-2.2.21-blue.svg?logo=kotlin)](http://kotlinlang.org)
 
 This is a port of [java-diff-utils](https://github.com/java-diff-utils/java-diff-utils) to Kotlin with multiplatform support.  
 All credit for the implementation goes to the original authors.