[MINOR][PySpark][SQL][DOC] Fix rowsBetween doc in Window

[viirya]

What changes were proposed in this pull request?

I suspect that the doc of rowsBetween methods in Scala and PySpark looks wrong.
Because:

scala> val df = Seq((1, "a"), (2, "a"), (3, "a"), (4, "a"), (5, "a"), (6, "a")).toDF("id", "category")                                                 
df: org.apache.spark.sql.DataFrame = [id: int, category: string]                                                                                       
                                                                                                                                                       
scala> val byCategoryOrderedById = Window.partitionBy('category).orderBy('id).rowsBetween(-1, 2)                                                       
byCategoryOrderedById: org.apache.spark.sql.expressions.WindowSpec = org.apache.spark.sql.expressions.WindowSpec@7f04de97                              
                                                                                                                                                       
scala> df.withColumn("sum", sum('id) over byCategoryOrderedById).show()                                                                                
+---+--------+---+                                                                                                                                     
| id|category|sum|                                                                                                                                     
+---+--------+---+                                                                                                                                     
|  1|       a|  6|              # sum from index 0 to (0 + 2): 1 + 2 + 3 = 6                                                                                                                      
|  2|       a| 10|              # sum from index (1 - 1) to (1 + 2): 1 + 2 + 3 + 4 = 10                                                                                                                       
|  3|       a| 14|                                                                                                                             
|  4|       a| 18|                                                                                                                                     
|  5|       a| 15|
|  6|       a| 11|
+---+--------+---+

So the frame (-1, 2) for row with index 5, as described in the doc, should range from index 4 to index 7.

How was this patch tested?

N/A, just doc change.

[viirya]

cc @HyukjinKwon @dongjoon-hyun

[SparkQA]

Test build #106474 has finished for PR 24864 at commit d072de5.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

LGTM

[HyukjinKwon]

Merged to master.

Had a conflict against branch-2.4 but I think we don't have to bother backport ..

[viirya]

Yea, I do think so. Thanks @HyukjinKwon