add xmpcore as direct dependency to pom

(otherwise it's looked up at pdfbox archive path and not found there)

pom.xml

@@ -626,6 +626,11 @@
             <artifactId>xercesImpl</artifactId>
             <version>2.11.0</version>
         </dependency>
+        <dependency>
+            <groupId>com.adobe.xmp</groupId>
+            <artifactId>xmpcore</artifactId>
+            <version>5.1.2</version>
+        </dependency>        
 
         <!-- special setup for dependencies not found in maven repository
         to installed in local repository -->