Update Doc/library/dbm.rst

Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>

Author: Yuki Kobayashi

Doc/library/dbm.rst

@@ -455,7 +455,7 @@ The :mod:`!dbm.dumb` module defines the following:
    .. method:: dumbdbm.sync()
 
       Synchronize the on-disk directory and data files.  This method is called
-      by the :meth:`Shelf.sync <shelve.Shelf.sync>` method.
+      by the :meth:`shelve.Shelf.sync` method.
 
    .. method:: dumbdbm.close()