revlog: fix docket.date_filepath docstring

This was copy-pasted too quickly.

Differential Revision: https://phab.mercurial-scm.org/D10786

mercurial/revlogutils/docket.py

@@ -145,7 +145,7 b' class RevlogDocket(object):'
         return b"%s-%s.idx" % (self._radix, self._index_uuid)
 
     def data_filepath(self):
-        """file path to the current index file associated to this docket"""
+        """file path to the current data file associated to this docket"""
         # very simplistic version at first
         if self._data_uuid is None:
             self._data_uuid = make_uid()