updates README in batch-job sample setting min Java v to 8

Author: csaethre19

spring-cloud-task-samples/batch-job/README.adoc

@@ -4,7 +4,7 @@ This is a Spring Cloud Task application that executes two simple Spring Batch Jo
 
 == Requirements:
 
-* Java 7 or Above
+* Java 8 or Above
 
 == Classes: