Upgrade to Groovy 2.5.11

Closes gh-21152

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

@@ -65,7 +65,7 @@
 		<elasticsearch.version>6.4.3</elasticsearch.version>
 		<glassfish-el.version>3.0.0</glassfish-el.version>
 		<glassfish-jaxb.version>2.3.1</glassfish-jaxb.version>
-		<groovy.version>2.5.9</groovy.version>
+		<groovy.version>2.5.11</groovy.version>
 		<gson.version>2.8.6</gson.version>
 		<h2.version>1.4.200</h2.version>
 		<hamcrest.version>1.3</hamcrest.version>