Fix typo. Pointed out by Finn Ellis on docs@.

Doc/library/userdict.rst

@@ -128,7 +128,7 @@ attribute:
    A real Python list object used to store the contents of the :class:`UserList`
    class.
 
-**Subclassing requirements:** Subclasses of :class:`UserList` are expect to
+**Subclassing requirements:** Subclasses of :class:`UserList` are expected to
 offer a constructor which can be called with either no arguments or one
 argument.  List operations which return a new sequence attempt to create an
 instance of the actual implementation class.  To do so, it assumes that the