[SPARK-23815]follow up. further improve comment

Author: Fangshi Li

core/src/main/scala/org/apache/spark/internal/io/HadoopMapReduceCommitProtocol.scala

@@ -190,8 +190,8 @@ class HadoopMapReduceCommitProtocol(
             // According to the official hadoop FileSystem API spec, delete op should assume
             // the destination is no longer present regardless of return value, thus we do not
             // need to double check if finalPartPath exists before rename.
-            // Also, in our case, delete should return false only when finalPartPath does not
-            // exist. When this happens, we need to take action only if parent of finalPartPath
+            // Also in our case, based on the spec, delete returns false only when finalPartPath
+            // does not exist. When this happens, we need to take action if parent of finalPartPath
             // also does not exist(e.g. the scenario described on SPARK-23815), because
             // FileSystem API spec on rename op says the rename dest(finalPartPath) must have
             // a parent that exists, otherwise we may get unexpected result on the rename.