fix build

Author: niedzielski

docs/capabilities/server/overview.md

@@ -40,6 +40,6 @@ Allows you to execute some actions, like posting or commenting, on behalf of the
 
 Allows you to specify how your interactive post is displayed on platforms that don't support Devvit, for example old.reddit.com
 
-## [Cache helper](./cache-helper.mdx)
+## [Cache helper](./cache-helper.md)
 
 Allows you to cache fetch requests on the server side, reducing the number of requests made to external APIs and improving performance.