Fix maxTaskFailures comment

If maxTaskFailures is 1, the task set is aborted after 1 task failure. Other documentation and the code supports this reading, I think it's just this comment that was off. It's easy to make this mistake — can you please double-check if I'm correct? Thanks!

Author: Daniel Darabos <darabos.daniel@gmail.com>

Closes #6621 from darabos/patch-2 and squashes the following commits:

dfebdec [Daniel Darabos] Fix comment.

core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala

@@ -46,7 +46,7 @@ import org.apache.spark.util.{Clock, SystemClock, Utils}
  *
  * @param sched           the TaskSchedulerImpl associated with the TaskSetManager
  * @param taskSet         the TaskSet to manage scheduling for
- * @param maxTaskFailures if any particular task fails more than this number of times, the entire
+ * @param maxTaskFailures if any particular task fails this number of times, the entire
  *                        task set will be aborted
  */
 private[spark] class TaskSetManager(