Downgrade to Groovy 2.4.13

There's an extra ClassLoader in the hierarchy of the TCCL in Groovy
2.4 vs Groovy 2.5 so we require an extra getParent() call to avoid
being able to load classes that are visible to the launched URL
class loader.

Closes gh-11745

spring-boot-project/spring-boot-cli/src/main/java/org/springframework/boot/cli/compiler/ExtendedGroovyClassLoader.java

 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -176,7 +176,7 @@ public class ExtendedGroovyClassLoader extends GroovyClassLoader {
 		DefaultScopeParentClassLoader(ClassLoader parent) {
 			super(parent);
 			this.groovyOnlyClassLoader = new URLClassLoader(getGroovyJars(parent),
-					parent.getParent());
+					parent.getParent().getParent());
 		}
 
 		private URL[] getGroovyJars(ClassLoader parent) {

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -53,7 +53,7 @@
 		<freemarker.version>2.3.27-incubating</freemarker.version>
 		<elasticsearch.version>5.6.6</elasticsearch.version>
 		<glassfish-el.version>3.0.0</glassfish-el.version>
-		<groovy.version>2.5.0-beta-2</groovy.version>
+		<groovy.version>2.4.13</groovy.version>
 		<gson.version>2.8.2</gson.version>
 		<h2.version>1.4.196</h2.version>
 		<hamcrest.version>1.3</hamcrest.version>