Bump com.github.johnrengelman.shadow from 7.1.2 to 8.1.1

Bumps com.github.johnrengelman.shadow from 7.1.2 to 8.1.1.

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

Signed-off-by: dependabot[bot] <support@github.com>

uhabits-server/build.gradle.kts

@@ -22,7 +22,7 @@ import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
 plugins {
     application
     id("kotlin")
-    id("com.github.johnrengelman.shadow") version "7.1.2"
+    id("com.github.johnrengelman.shadow") version "8.1.1"
 }