Update Word2Vec.scala

Added javadoc

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

@@ -121,14 +121,17 @@ class Word2Vec extends Serializable with Logging {
 
   /** context words from [-window, window] */
   private val window = 5
-
-/** minimum frequency to consider a vocabulary word */
-private var minCount = 5
-
-def setMinCount(minCount: Int): this.type = {
-this.minCount = minCount
-this
-}
+
+  /** minimum frequency to consider a vocabulary word */
+  private var minCount = 5
+
+  /** Sets the minimum frequency a token must appear to be included in the word2vec model's 
+    * vocabulary (default: 5).
+    */
+  def setMinCount(minCount: Int): this.type = {
+  this.minCount = minCount
+  this
+  }
 
   private var trainWordsCount = 0
   private var vocabSize = 0