[docs] Typo in Python Documentation

[Daryl Klakouski]

Hi,

In the Python 3 documentation, section 4.7.1, in the bit about
str.zfill(width)
(https://docs.python.org/3/library/stdtypes.html#str.zfill), there is
a missing close parenthesis in the second sentence, at "( ' + ' / ' -
' ".