Upgrade versions-maven-plugin 2.20.1 -> 2.21.0 (#2071)

See:
- https://github.com/mojohaus/versions/releases/tag/2.21.0
- mojohaus/versions@2.20.1...2.21.0

Author: Picnic-DevPla-Bot

pom.xml

@@ -1507,7 +1507,7 @@
                 <plugin>
                     <groupId>org.codehaus.mojo</groupId>
                     <artifactId>versions-maven-plugin</artifactId>
-                    <version>2.20.1</version>
+                    <version>2.21.0</version>
                     <configuration>
                         <updateBuildOutputTimestampPolicy>never</updateBuildOutputTimestampPolicy>
                     </configuration>