Bump com.github.johnrengelman.shadow from 6.1.0 to 8.1.1 (#6)

Bumps com.github.johnrengelman.shadow from 6.1.0 to 8.1.1.

---
updated-dependencies:
- dependency-name: com.github.johnrengelman.shadow
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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build.gradle.kts

@@ -1,7 +1,7 @@
 plugins {
     java
     `maven-publish`
-    id("com.github.johnrengelman.shadow") version "6.1.0"
+    id("com.github.johnrengelman.shadow") version "8.1.1"
 }
 
 group = "com.iridium"