Upgrade to Groovy 2.4.15

Closes gh-12730

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -78,7 +78,7 @@
 		<gemfire.version>8.2.8</gemfire.version>
 		<glassfish-el.version>3.0.0</glassfish-el.version>
 		<gradle.version>2.9</gradle.version>
-		<groovy.version>2.4.14</groovy.version>
+		<groovy.version>2.4.15</groovy.version>
 		<gson.version>2.8.2</gson.version>
 		<h2.version>1.4.197</h2.version>
 		<hamcrest.version>1.3</hamcrest.version>