Bump XStream Version. Fixes #747

Author: Thomas Oster

pom.xml

@@ -84,7 +84,7 @@
         <dependency>
             <groupId>com.thoughtworks.xstream</groupId>
             <artifactId>xstream</artifactId>
-            <version>1.4.19</version>
+            <version>1.4.21</version>
             <type>jar</type>
         </dependency>
         <dependency>