Update Jena Version to 5.6.0

Also refactors POM file to use a 'jena.version' string to simplify
future updates

Signed-off-by: Gary O'Neall <gary@sourceauditor.com>

Author: goneall

pom.xml

@@ -16,6 +16,7 @@
 	<sonar.projectKey>spdx-rdf-store</sonar.projectKey>
 	<dependency-check-maven.version>12.1.8</dependency-check-maven.version>
 	<javadoc.opts>-Xdoclint:none</javadoc.opts>
+	  <jena.version>5.6.0</jena.version>
   </properties>
     <licenses>
 		<license>
@@ -127,17 +128,17 @@
     <dependency>
     	<groupId>org.apache.jena</groupId>
     	<artifactId>jena-core</artifactId>
-    	<version>5.5.0</version>
+    	<version>${jena.version}</version>
     </dependency>
     <dependency>
     	<groupId>org.apache.jena</groupId>
     	<artifactId>jena-arq</artifactId>
-    	<version>5.5.0</version>
+    	<version>${jena.version}</version>
     </dependency>
     <dependency>
     	<groupId>org.apache.jena</groupId>
     	<artifactId>jena-base</artifactId>
-    	<version>5.5.0</version>
+    	<version>${jena.version}</version>
     </dependency>
   </dependencies>
     <build>