Bump xstream from 1.4.15 to 1.4.20

Bumps [xstream](https://github.com/x-stream/xstream) from 1.4.15 to 1.4.20.
- [Release notes](https://github.com/x-stream/xstream/releases)
- [Commits](https://github.com/x-stream/xstream/commits)

---
updated-dependencies:
- dependency-name: com.thoughtworks.xstream:xstream
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

pom.xml

@@ -398,7 +398,7 @@
 						<dependency>
 							<groupId>com.thoughtworks.xstream</groupId>
 							<artifactId>xstream</artifactId>
-							<version>1.4.15</version>
+							<version>1.4.20</version>
 						</dependency>
 					</dependencies>
 				</plugin>