When we were implementing the feature known as "Retryable Writes" we chose the spelling with a "y", but there's still a lot of code in the mongo repository that spells it with an "i". Let's finish updating the spelling, for the sake of consistency, and so that Docs, Marketing, and Engineering spell it the same.

... in case anyone doubts that we chose "retryable" as the spelling, see:

https://docs.mongodb.com/manual/core/retryable-writes/
https://github.com/mongodb/specifications/blob/master/source/retryable-writes/retryable-writes.rst
https://www.prnewswire.com/news-releases/mongodb-36-empowers-enterprises-and-developers-to-move-at-the-speed-of-data-300551705.html

Assigning to Sharding since I think they wrote the first code handling the "Retriable" error category.