Replace deprecated `first` with `head`.

core/src/main/scala/spark/CoGroupedRDD.scala

@@ -26,7 +26,7 @@ class CoGroupAggregator extends Aggregator[Any, Any, ArrayBuffer[Any]] (
 )
 
 class CoGroupedRDD[K](rdds: Seq[RDD[(_, _)]], part: Partitioner)
-extends RDD[(K, Seq[Seq[_]])](rdds.first.context) with Logging {
+extends RDD[(K, Seq[Seq[_]])](rdds.head.context) with Logging {
   val aggr = new CoGroupAggregator
   
   override val dependencies = {
@@ -45,7 +45,7 @@ extends RDD[(K, Seq[Seq[_]])](rdds.first.context) with Logging {
   }
   
   @transient val splits_ : Array[Split] = {
-    val firstRdd = rdds.first
+    val firstRdd = rdds.head
     val array = new Array[Split](part.numPartitions)
     for (i <- 0 until array.size) {
       array(i) = new CoGroupSplit(i, rdds.zipWithIndex.map { case (r, j) =>

core/src/main/scala/spark/DAGScheduler.scala

@@ -237,7 +237,7 @@ private trait DAGScheduler extends Scheduler with Logging {
                 if (stage.shuffleDep != None) {
                   mapOutputTracker.registerMapOutputs(
                     stage.shuffleDep.get.shuffleId,
-                    stage.outputLocs.map(_.first).toArray)
+                    stage.outputLocs.map(_.head).toArray)
                 }
                 updateCacheLocs()
                 val newlyRunnable = new ArrayBuffer[Stage]