downgrade plexus-xml from 4 to 3: keep Maven 3 compatibility

Author: hboutemy

README.md

@@ -16,4 +16,4 @@ mvn -Preporting verify site site:stage scm-publish:publish-scm
 
 Starting with version 4, XML classes (in `org.codehaus.plexus.util.xml` and `org.codehaus.plexus.util.xml.pull`) have been extracted to a separate [`plexus-xml`](https://github.com/codehaus-plexus/plexus-xml/) library: if you need them, just use this new artifact.
 
-`plexus-utils` 4 keeps an optional dependency on `plexus-xml` to keep compatibility with the few XML-oriented methods of `ReaderFactory` and `WriterFactory`: these classes are deprecated, you should migrate as explained in javadoc.
+`plexus-utils` 4 keeps an optional dependency on `plexus-xml` 3 to keep compatibility with the few XML-oriented methods of `ReaderFactory` and `WriterFactory`: these classes are deprecated, you should migrate as explained in javadoc. And keep `plexus-xml` to 3 if you want Maven 3 compatibility, as `plexus-xml` 4 works only in Maven 4.

pom.xml

@@ -56,7 +56,8 @@ limitations under the License.
     <dependency>
       <groupId>org.codehaus.plexus</groupId>
       <artifactId>plexus-xml</artifactId>
-      <version>4.0.2</version>
+      <version>3.0.0</version>
+      <!-- this dependency is optional, only necessary for deprecated Reader/WriterFactory.newXmlReader/Writer(...) -->
       <optional>true</optional>
     </dependency>
     <dependency>