fix: Fixed typo (#1542)

Author: fabriziofiorucci

content/nginx/admin-guide/content-cache/content-caching.md

@@ -56,7 +56,7 @@ There are two additional NGINX processes involved in caching:
 
   - `loader_threshold` – Duration of an iteration, in milliseconds (by default, `200`)
   - `loader_files` – Maximum number of items loaded during one iteration (by default, `100`)
-  - `loader_sleeps` – Delay between iterations, in milliseconds (by default, `50`)
+  - `loader_sleep` – Delay between iterations, in milliseconds (by default, `50`)
 
 In the following example, iterations last `300` milliseconds or until `200` items have been loaded: