Replace unreleased changelog plugin 2.2.1 with 2.2.0

Builds on the ci.jenkins.io master branch fail with the message:

> Could not find artifact se.bjurr.gitchangelog:git-changelog-maven-plugin:jar:2.2.1

https://mvnrepository.com/artifact/se.bjurr.gitchangelog/git-changelog-maven-plugin
reports that the most recent release is 2.2.0, not 2.2.1.

Switch to 2.2.0 instead of 2.2.1

Author: MarkEWaite

pom.xml

@@ -15,7 +15,7 @@
         <maven.javadoc.skip>true</maven.javadoc.skip>
         <violations.version>2.2.0</violations.version>
         <changelog-lib>2.4.1</changelog-lib>
-        <changelog-plugin>2.2.1</changelog-plugin>
+        <changelog-plugin>2.2.0</changelog-plugin>
     </properties>
 
     <groupId>de.wellnerbou.jenkins</groupId>