Use Correct License Name "Plexus"

The pom.xml states that dom4j is using the BSD-3-Clause license, but the license text does not match that statement.

The license text matches the "Plexus Classworlds License".
The SPDX identifier is "Plexus", which would be the recomended entry for the name field in the pom.

https://spdx.org/licenses/Plexus.html

build.gradle

@@ -76,7 +76,7 @@ publishing {
                 url = 'http://dom4j.github.io/'
                 licenses {
                     license {
-                        name = 'BSD 3-clause New License'
+                        name = 'Plexus'
                         url = 'https://github.com/dom4j/dom4j/blob/master/LICENSE'
                     }
                 }