GROOVY-8993: Bump spotbugs gradle plugin to 1.6.9(closes #879)
GROOVY-8993: Bump spotbugs gradle plugin to 1.6.9(closes #879)

jwagenleitner/groovy,shils/groovy,paulk-asert/incubator-groovy,paulk-asert/incubator-groovy,jwagenleitner/groovy,apache/groovy,paulk-asert/groovy,paulk-asert/groovy,apache/incubator-groovy,armsargis/groovy,armsargis/groovy,jwagenleitner/incubator-groovy,apache/incubator-groovy,shils/incubator-groovy,shils/groovy,armsargis/groovy,apache/incubator-groovy,apache/groovy,jwagenleitner/incubator-groovy,shils/incubator-groovy,shils/groovy,shils/incubator-groovy,shils/groovy,jwagenleitner/incubator-groovy,paulk-asert/incubator-groovy,jwagenleitner/groovy,armsargis/groovy,apache/incubator-groovy,jwagenleitner/incubator-groovy,paulk-asert/groovy,shils/incubator-groovy,paulk-asert/incubator-groovy,apache/groovy,paulk-asert/groovy,jwagenleitner/groovy,apache/groovy,paulk-asert/incubator-groovy