Added missing right bracket (reported by Daryl Klakouski)

Doc/library/stdtypes.rst

@@ -2008,7 +2008,7 @@ expression support in the :mod:`re` module).
 .. method:: str.zfill(width)
 
    Return a copy of the string left filled with ASCII ``'0'`` digits to
-   make a string of length *width*. A leading sign prefix (``'+'``/``'-'``
+   make a string of length *width*. A leading sign prefix (``'+'``/``'-'``)
    is handled by inserting the padding *after* the sign character rather
    than before. The original string is returned if *width* is less than
    or equal to ``len(s)``.