Add spock dependencies to dependency-management.properties

Spring Boot removed sock from its dependency management via
https://github.com/spring-projects/spring-boot/issues/9043

This commit adds spock to this project's dependency management

gradle/dependency-management.properties

@@ -10,3 +10,5 @@ org.powermock\:powermock-module-junit4-common=1.6.2
 org.powermock\:powermock-module-junit4=1.6.2
 org.powermock\:powermock-reflect=1.6.2
 org.python\:jython=2.5.0
+org.spockframework\:spock-core=1.0-groovy-2.4
+org.spockframework\:spock-spring=1.0-groovy-2.4