Bump xstream in /tcmsteamsbuildnotifier-web-ui

Bumps [xstream](https://github.com/x-stream/xstream) from 1.4.10-java7 to 1.4.15.
- [Release notes](https://github.com/x-stream/xstream/releases)
- [Commits](https://github.com/x-stream/xstream/commits)

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

tcmsteamsbuildnotifier-web-ui/pom.xml

@@ -209,7 +209,7 @@
         <dependency>
             <groupId>com.thoughtworks.xstream</groupId>
             <artifactId>xstream</artifactId>
-            <version>1.4.10-java7</version>
+            <version>1.4.15</version>
             <scope>provided</scope>
         </dependency>