Update checkstyle to version 6.19

Change-Id: I32787f2a5f4f4b17fd4cdcf9bd2eb3903dcecfff
diff --git a/core/common/src/test/java/org/onosproject/store/trivial/SimpleGroupStore.java b/core/common/src/test/java/org/onosproject/store/trivial/SimpleGroupStore.java
index f3f0bd7..c55d009 100644
--- a/core/common/src/test/java/org/onosproject/store/trivial/SimpleGroupStore.java
+++ b/core/common/src/test/java/org/onosproject/store/trivial/SimpleGroupStore.java
@@ -416,7 +416,7 @@
                     Optional<GroupBucket> matchingBucket =
                             existing.buckets().buckets()
                             .stream()
-                            .filter((existingBucket)->(existingBucket.equals(bucket)))
+                            .filter((existingBucket) -> (existingBucket.equals(bucket)))
                             .findFirst();
                     if (matchingBucket.isPresent()) {
                         ((StoredGroupBucketEntry) matchingBucket.