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] <[email protected]>

build.gradle

@@ -8,7 +8,7 @@ buildscript {
     }
 
     dependencies {
-        classpath "com.github.johnrengelman:shadow:7.1.2"
+        classpath "com.github.johnrengelman:shadow:8.1.1"
         classpath "net.minecraftforge.gradle:ForgeGradle:6.+"
         classpath "org.spongepowered:mixingradle:0.7-SNAPSHOT"
         classpath "xyz.wagyourtail.jvmdowngrader:gradle-plugin:1.0.0"