minor updates to word2vec

Author: mengxr

mllib/src/main/scala/org/apache/spark/mllib/feature/Word2Vec.scala

@@ -30,7 +30,6 @@ import org.apache.spark.SparkContext._
 import org.apache.spark.annotation.Experimental
 import org.apache.spark.api.java.JavaRDD
 import org.apache.spark.mllib.linalg.{Vector, Vectors}
-import org.apache.spark.mllib.rdd.RDDFunctions._
 import org.apache.spark.rdd._
 import org.apache.spark.util.Utils
 import org.apache.spark.util.random.XORShiftRandom
@@ -285,9 +284,9 @@ class Word2Vec extends Serializable with Logging {
 
     val newSentences = sentences.repartition(numPartitions).cache()
     val initRandom = new XORShiftRandom(seed)
-    var syn0Global =
+    val syn0Global =
       Array.fill[Float](vocabSize * vectorSize)((initRandom.nextFloat() - 0.5f) / vectorSize)
-    var syn1Global = new Array[Float](vocabSize * vectorSize)
+    val syn1Global = new Array[Float](vocabSize * vectorSize)
     var alpha = startingAlpha
     for (k <- 1 to numIterations) {
       val partial = newSentences.mapPartitionsWithIndex { case (idx, iter) =>