ingest: make concrete processor impl final, like all other processor concrete impls.

Author: martijnvg

core/src/main/java/org/elasticsearch/ingest/processor/SplitProcessor.java

@@ -34,7 +34,7 @@
  * New field value will be an array containing all of the different extracted items.
  * Throws exception if the field is null or a type other than string.
  */
-public class SplitProcessor extends AbstractProcessor {
+public final class SplitProcessor extends AbstractProcessor {
 
     public static final String TYPE = "split";