Bump versions-maven-plugin from 2.7 to 2.8.1 (#10)

Bumps [versions-maven-plugin](https://github.com/mojohaus/versions-maven-plugin) from 2.7 to 2.8.1.
- [Release notes](https://github.com/mojohaus/versions-maven-plugin/releases)
- [Changelog](https://github.com/mojohaus/versions-maven-plugin/blob/master/ReleaseNotes.md)
- [Commits](https://github.com/mojohaus/versions-maven-plugin/compare/versions-maven-plugin-2.7...versions-maven-plugin-2.8.1)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
diff --git a/pom.xml b/pom.xml
index b86a5dc..003b4ab 100644
--- a/pom.xml
+++ b/pom.xml
@@ -156,7 +156,7 @@
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>versions-maven-plugin</artifactId>
         <!-- Version 2.2 causes an NPE with Maven 3.3.9 -->
-        <version>2.7</version>
+        <version>2.8.1</version>
       </plugin>
       <plugin>
         <groupId>com.github.spotbugs</groupId>