minor symfony#9975 Fix typo in the Twig article (rvuongdav)

This PR was merged into the 2.8 branch.

Discussion
----------

Fix typo in the Twig article

Minor typo found in the Twig article about the `internal_format` option.

Commits
-------

3cf4934 Fix typo in the Twig article

Author: javiereguiluz

reference/configuration/twig.rst

@@ -128,7 +128,7 @@ format
 The format used by the ``date`` filter to display values when no specific format
 is passed as argument.
 
-internal_format
+interval_format
 ...............
 
 **type**: ``string`` **default**: ``%d days``