Update Muatation score badge version

README.md

@@ -1,4 +1,4 @@
-[![Mutation testing badge](https://img.shields.io/endpoint?style=flat&url=https%3A%2F%2Fbadge-api.stryker-mutator.io%2Fgithub.com%2Fpatchlevel%2Fevent-sourcing%2F3.0.x)](https://dashboard.stryker-mutator.io/reports/github.com/patchlevel/event-sourcing/3.0.x)
+[![Mutation testing badge](https://img.shields.io/endpoint?style=flat&url=https%3A%2F%2Fbadge-api.stryker-mutator.io%2Fgithub.com%2Fpatchlevel%2Fevent-sourcing%2F3.8.x)](https://dashboard.stryker-mutator.io/reports/github.com/patchlevel/event-sourcing/3.8.x)
 [![Type Coverage](https://shepherd.dev/github/patchlevel/event-sourcing/coverage.svg)](https://shepherd.dev/github/patchlevel/event-sourcing)
 [![Latest Stable Version](https://poser.pugx.org/patchlevel/event-sourcing/v)](//packagist.org/packages/patchlevel/event-sourcing)
 [![License](https://poser.pugx.org/patchlevel/event-sourcing/license)](//packagist.org/packages/patchlevel/event-sourcing)