fix to minor accidental update

Author: LucaCanali

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -27,7 +27,7 @@ import scala.collection.JavaConverters._
 import scala.collection.Map
 import scala.collection.mutable.HashMap
 import scala.language.implicitConversions
-import scala.reflect.{ClassTag, classTag}
+import scala.reflect.{classTag, ClassTag}
 import scala.util.control.NonFatal
 import com.google.common.collect.MapMaker
 import org.apache.hadoop.conf.Configuration