Fix dependency scope for AssertJ

Prior to this commit the dependency scope was not set and thus the default 
provided would apply. We now explicitly set it to a scope of test

spring-batch-excel/pom.xml

@@ -103,6 +103,7 @@
 			<groupId>org.assertj</groupId>
 			<artifactId>assertj-core</artifactId>
 			<version>${assertj.version}</version>
+			<scope>test</scope>
 		</dependency>
 		<dependency>
 			<groupId>org.apache.logging.log4j</groupId>