Merge pull request #173 from GateNLP/dependabot/maven/com.thoughtworks.xstream-xstream-1.4.21

Bump com.thoughtworks.xstream:xstream from 1.4.20 to 1.4.21

Author: ianroberts

pom.xml

@@ -410,7 +410,7 @@
 		<dependency>
 			<groupId>com.thoughtworks.xstream</groupId>
 			<artifactId>xstream</artifactId>
-			<version>1.4.20</version>
+			<version>1.4.21</version>
 			<scope>compile</scope>
 			<exclusions>
 				<!-- we will pull in the full xpp3 so we don't need these -->