[MINOR][DOC] Update the condition description of serialized shuffle

core/src/main/scala/org/apache/spark/shuffle/sort/SortShuffleManager.scala

@@ -33,10 +33,10 @@ import org.apache.spark.shuffle._
  * Sort-based shuffle has two different write paths for producing its map output files:
  *
  *  - Serialized sorting: used when all three of the following conditions hold:
- *    1. The shuffle dependency specifies no aggregation or output ordering.
+ *    1. The shuffle dependency specifies no map-side combine.
  *    2. The shuffle serializer supports relocation of serialized values (this is currently
  *       supported by KryoSerializer and Spark SQL's custom serializers).
- *    3. The shuffle produces fewer than 16777216 output partitions.
+ *    3. The shuffle produces fewer than or equal to 16777216 output partitions.
  *  - Deserialized sorting: used to handle all other cases.
  *
  * -----------------------