Merge pull request #154 from humanmade/backport-153-to-v4-branch

[Backport v4-branch] v4 upgrade guide: fix elasticpress index parameter

other-docs/guides/upgrading/v4.md

@@ -59,7 +59,7 @@ We recommend reindexing as soon as possible to take advantage of the new languag
 wp --url=... elasticpress index --setup --network-wide
 ```
 
-(Some sites with large posts or large metadata sizes may encounter errors while reindexing which reference the payload size. Try passing `--per-page 200` and other smaller numbers to decrease the chunk size, or contact the Altis Cloud team for advice.)
+(Some sites with large posts or large metadata sizes may encounter errors while reindexing which reference the payload size. Try passing `--posts-per-page 200` and other smaller numbers to decrease the chunk size, or contact the Altis Cloud team for advice.)
 
 
 ## Headline Features