Corrected learn_cache_key() signature in docs.
Follow up to
@@ -97,7 +97,7 @@ need to distinguish caches by the ``Accept-language`` header.
If there is no headerlist stored, the page needs to be rebuilt, so this
function returns ``None``.
-.. function:: learn_cache_key(request, response, cache_timeout=None, key_prefix=None)
+.. function:: learn_cache_key(request, response, cache_timeout=None, key_prefix=None, cache=None)
Learns what headers to take into account for some request path from the
response object. It stores those headers in a global path registry so that
