Update XStream

Author: stefanius

pom.xml

@@ -178,7 +178,7 @@
                     <dependency>
                         <groupId>com.thoughtworks.xstream</groupId>
                         <artifactId>xstream</artifactId>
-                        <version>1.4.15</version>
+                        <version>1.4.21</version>
                     </dependency>
                 </dependencies>
             </plugin>