Updated for Spring 5 baseline

The new Spring 5 baseline consists of Spring 5, Hibernate 5, and Java 8.
This commit addresses any changes to create a successful build of Spring
Batch under those guidances.  Further commits will be coming to address
Java 8 specifics as areas of the project are touched.

Resolves BATCH-2536

spring-batch-integration/src/main/java/org/springframework/batch/integration/partition/MessageChannelPartitionHandler.java

@@ -181,7 +181,7 @@ public class MessageChannelPartitionHandler implements PartitionHandler, Initial
 	 * @param messages the messages to be aggregated
 	 * @return the list as it was passed in
 	 */
-	@Aggregator(sendPartialResultsOnExpiry = true)
+	@Aggregator(sendPartialResultsOnExpiry = "true")
 	public List<?> aggregate(@Payloads List<?> messages) {
 		return messages;
 	}