Update checkstyle to version 6.19

Change-Id: I32787f2a5f4f4b17fd4cdcf9bd2eb3903dcecfff
diff --git a/incubator/store/src/main/java/org/onosproject/incubator/store/virtual/impl/SimpleVirtualGroupStore.java b/incubator/store/src/main/java/org/onosproject/incubator/store/virtual/impl/SimpleVirtualGroupStore.java
index b6be85d..98e3d87 100644
--- a/incubator/store/src/main/java/org/onosproject/incubator/store/virtual/impl/SimpleVirtualGroupStore.java
+++ b/incubator/store/src/main/java/org/onosproject/incubator/store/virtual/impl/SimpleVirtualGroupStore.java
@@ -412,7 +412,7 @@
                     Optional<GroupBucket> matchingBucket =
                             existing.buckets().buckets()
                                     .stream()
-                                    .filter((existingBucket)->(existingBucket.equals(bucket)))
+                                    .filter((existingBucket) -> (existingBucket.equals(bucket)))
                                     .findFirst();
                     if (matchingBucket.isPresent()) {
                         ((StoredGroupBucketEntry) matchingBucket.