[SPARK-11582][MLLIB] specifying pmml version attribute =4.2 in the root node of pmml model

The current pmml models generated do not specify the pmml version in its root node. This is a problem when using this pmml model in other tools because they expect the version attribute to be set explicitly. This fix adds the pmml version attribute to the generated pmml models and specifies its value as 4.2.

Author: fazlan-nazeem <[email protected]>

Closes #9558 from fazlan-nazeem/master.

(cherry picked from commit 9b88e1d)
Signed-off-by: Xiangrui Meng <[email protected]>

Author: fazlan-nazeem

mllib/src/main/scala/org/apache/spark/mllib/pmml/export/PMMLModelExport.scala

@@ -32,6 +32,7 @@ private[mllib] trait PMMLModelExport {
   @BeanProperty
   val pmml: PMML = new PMML
 
+  pmml.setVersion("4.2")
   setHeader(pmml)
 
   private def setHeader(pmml: PMML): Unit = {