[HOTFIX] [TYPO] Fix typo in apache#6546

Author: Andrew Or

core/src/test/scala/org/apache/spark/ExternalShuffleServiceSuite.scala

@@ -56,11 +56,11 @@ class ExternalShuffleServiceSuite extends ShuffleSuite with BeforeAndAfterAll {
     sc.env.blockManager.shuffleClient.getClass should equal(classOf[ExternalShuffleClient])
 
     // In a slow machine, one slave may register hundreds of milliseconds ahead of the other one.
-    // If we don't wait for all salves, it's possible that only one executor runs all jobs. Then
+    // If we don't wait for all slaves, it's possible that only one executor runs all jobs. Then
     // all shuffle blocks will be in this executor, ShuffleBlockFetcherIterator will directly fetch
     // local blocks from the local BlockManager and won't send requests to ExternalShuffleService.
     // In this case, we won't receive FetchFailed. And it will make this test fail.
-    // Therefore, we should wait until all salves are up
+    // Therefore, we should wait until all slaves are up
     sc.jobProgressListener.waitUntilExecutorsUp(2, 10000)
 
     val rdd = sc.parallelize(0 until 1000, 10).map(i => (i, 1)).reduceByKey(_ + _)