improve sentence re: content-disposition header

The correct English term would be either '...is more involved', or '...involves more effort'

Author: nealio82

components/http_foundation.rst

@@ -534,7 +534,7 @@ Serving Files
 
 When sending a file, you must add a ``Content-Disposition`` header to your
 response. While creating this header for basic file downloads is straightforward,
-using non-ASCII filenames is more involving. The
+using non-ASCII filenames is more involved. The
 :method:`Symfony\\Component\\HttpFoundation\\HeaderUtils::makeDisposition`
 abstracts the hard work behind a simple API::