POM: Apply ${xz.version} as appropriate.

Change-Id: I0ac6db1e3e5530221316db28c12015e9f4e9c18b
diff --git a/jgvariant-parent/pom.xml b/jgvariant-parent/pom.xml
index 92b7e07..9c6f302 100644
--- a/jgvariant-parent/pom.xml
+++ b/jgvariant-parent/pom.xml
@@ -119,7 +119,7 @@
       <dependency>
         <groupId>org.tukaani</groupId>
         <artifactId>xz</artifactId>
-        <version>1.9</version>
+        <version>${xz.version}</version>
       </dependency>
 
       <!-- Testing -->