Fix non-canonical links to jQuery.ajax

Thanks to WordPress, each of these works, but they also end up
indexed in Typesense (and in Algolia) as duplicate entries with
slightly differently cased URLs.

Avoid the duplication by making the links consistent.

Ref jquery/api.jquery.com@e7c8ccd.

Author: Krinkle

pages/upgrade-guide/3.0.md

@@ -74,7 +74,7 @@ https://github.com/jquery/jquery/issues/1732
 
 #### Feature: New signature for jQuery.get() AND jQuery.post()
 
-jQuery 3 adds a new signature for the `jQuery.get()` and the `jQuery.post()` functions by adding a `settings` parameter. It's an object that can possess many properties and its the same object that you can provide to [`jQuery.ajax()`](https://api.jquery.com/jquery.ajax/#jQuery-ajax-settings).
+jQuery 3 adds a new signature for the `jQuery.get()` and the `jQuery.post()` functions by adding a `settings` parameter. It's an object that can possess many properties and its the same object that you can provide to [`jQuery.ajax()`](https://api.jquery.com/jQuery.ajax/#jQuery-ajax-settings).
 
 https://github.com/jquery/jquery/issues/1986