Minor nit style cleanup in GraphX.

graphx/src/main/scala/org/apache/spark/graphx/VertexRDD.scala

@@ -68,7 +68,7 @@ abstract class VertexRDD[VD](
    * Provides the `RDD[(VertexId, VD)]` equivalent output.
    */
   override def compute(part: Partition, context: TaskContext): Iterator[(VertexId, VD)] = {
-    firstParent[ShippableVertexPartition[VD]].iterator(part, context).next.iterator
+    firstParent[ShippableVertexPartition[VD]].iterator(part, context).next().iterator
   }
 
   /**