Switch to Shadow plugin fork

This commit fixes to a fork of the shadow plugin that fixes support
with recent Gradle releases.

See https://github.com/johnrengelman/shadow/pull/876

build.gradle

@@ -5,8 +5,8 @@ plugins {
 	id 'org.jetbrains.dokka' version '1.8.20'
 	id 'com.github.ben-manes.versions' version '0.51.0'
 	id 'com.github.bjornvester.xjc' version '1.8.2' apply false
-	id 'com.github.johnrengelman.shadow' version '8.1.1' apply false
 	id 'de.undercouch.download' version '5.4.0'
+	id 'io.github.goooler.shadow' version '8.1.8' apply false
 	id 'me.champeau.jmh' version '0.7.2' apply false
 	id 'me.champeau.mrjar' version '0.1.1'
 }

gradle/spring-module.gradle

@@ -3,7 +3,7 @@ apply plugin: 'org.springframework.build.conventions'
 apply plugin: 'org.springframework.build.optional-dependencies'
 // Uncomment the following for Shadow support in the jmhJar block.
 // Currently commented out due to ZipException: archive is not a ZIP archive
-// apply plugin: 'com.github.johnrengelman.shadow'
+// apply plugin: 'io.github.goooler.shadow'
 apply plugin: 'me.champeau.jmh'
 apply from: "$rootDir/gradle/publications.gradle"