Upgraded to Groovy 2.5.15

Author: musketyr

gradle.properties

@@ -51,7 +51,7 @@ micronaut.worker.version = 1.1.4
 # external
 micronaut.version = 1.3.7
 spock.version = 1.3-groovy-2.5
-groovy.version = 2.5.14
+groovy.version = 2.5.15
 grails.version = 4.0.10
 aws.sdk.version = 1.11.1020
 aws.sdk.v2.version = 2.16.63