Add language version attribute

Test Plan: mvn test

Reviewers: jmsotuyo

Reviewed By: jmsotuyo

Subscribers: jmsotuyo

Differential Revision: http://ph.monits.com/D12205

pmd-java/src/main/resources/rulesets/java/clone.xml

@@ -130,6 +130,7 @@ public class MyClass {
 
     <rule name="CloneMethodReturnTypeMustMatchClassName"
         language="java"
+        minimumLanguageVersion="1.5"
         since="5.4.0"
         message="The return type of the clone() method must be the class name when implements Cloneable"
         class="net.sourceforge.pmd.lang.rule.XPathRule"