Fix typo in requests.md

Author: k4nar

docs/api-guide/requests.md

@@ -38,7 +38,7 @@ For clarity inside your code, we recommend using `request.query_params` instead
 
 ## .DATA and .FILES
 
-The old-style version 2.x `request.data` and `request.FILES` attributes are still available, but are now pending deprecation in favor of the unified `request.data` attribute.
+The old-style version 2.x `request.DATA` and `request.FILES` attributes are still available, but are now pending deprecation in favor of the unified `request.data` attribute.
 
 ## .QUERY_PARAMS