Fixed #9734 -- Typo fix in the custom fields documentation, pointed out by

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Creating custom fields requires a bit of attention to detail. To make things

easier to follow, we'll use a consistent example throughout this document.

Suppose you have a Python object representing the deal of cards in a hand of

Bridge_. (Don't worry, you don't know how to play Bridge to follow this

example. You only need to know that 52 cards are dealt out equally to four

players, who are traditionally called *north*, *east*, *south* and *west*.)

Our class looks something like this::

easier to follow, we'll use a consistent example throughout this document:

wrapping a Python object representing the deal of cards in a hand of Bridge_.

Don't worry, you don't have know how to play Bridge to follow this example.

You only need to know that 52 cards are dealt out equally to four players, who

are traditionally called *north*, *east*, *south* and *west*.  Our class looks

something like this::

    class Hand(object):

        def __init__(self, north, east, south, west):