Upgrade Spring Batch dependency to 2.2.6

Fixes gh-720

Author: Phillip Webb

spring-boot-dependencies/pom.xml

@@ -82,7 +82,7 @@
 		<spock.version>0.7-groovy-2.0</spock.version>
 		<spring.version>4.0.3.RELEASE</spring.version>
 		<spring-integration.version>3.0.1.RELEASE</spring-integration.version>
-		<spring-batch.version>2.2.5.RELEASE</spring-batch.version>
+		<spring-batch.version>2.2.6.RELEASE</spring-batch.version>
 		<spring-data-jpa.version>1.5.1.RELEASE</spring-data-jpa.version>
 		<spring-data-mongodb.version>1.4.1.RELEASE</spring-data-mongodb.version>
 		<spring-data-redis.version>1.1.1.RELEASE</spring-data-redis.version>