Bump org.apache.maven:maven-core from 3.0 to 3.8.1 in /xml-maven-plugin

Bumps [org.apache.maven:maven-core](https://github.com/apache/maven) from 3.0 to 3.8.1.
- [Release notes](https://github.com/apache/maven/releases)
- [Commits](apache/maven@maven-3.0...maven-3.8.1)

---
updated-dependencies:
- dependency-name: org.apache.maven:maven-core
  dependency-type: direct:production
...

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

xml-maven-plugin/pom.xml

@@ -31,7 +31,7 @@
     Maven Plugin for general XML-related tasks, specializing in validation and transformation of XML documents.
   </description>
   <properties>
-    <maven.version>3.0</maven.version>
+    <maven.version>3.8.1</maven.version>
   </properties>
   <prerequisites>
     <maven>${maven.version}</maven>