Bump xstream from 1.3.1 to 1.4.6 in /struts2-fileupload-plugin

Bumps xstream from 1.3.1 to 1.4.6.

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/struts2-fileupload-plugin/pom.xml b/struts2-fileupload-plugin/pom.xml
index d970886..ad8089a 100644
--- a/struts2-fileupload-plugin/pom.xml
+++ b/struts2-fileupload-plugin/pom.xml
@@ -48,7 +48,7 @@
         <dependency>
             <groupId>com.thoughtworks.xstream</groupId>
             <artifactId>xstream</artifactId>
-            <version>1.3.1</version>
+            <version>1.4.6</version>
         </dependency>
 
         <dependency>