DOC: update the pandas.DataFrame.plot.area docstring
- [x] PR title is "DOC: update the pandas.DataFrame.plot.area docstring"
- [x] The validation script passes: `scripts/validate_docstrings.py pandas.DataFrame.plot.area`
- [x] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] The html version looks good: `python doc/make.py --single pandas.DataFrame.plot.area`
- [x] It has been proofread on language by another sprint participant

```
################################################################################
#################### Docstring (pandas.DataFrame.plot.area) ####################
################################################################################

Draw an area plot of the input series using matplotlib.

An area plot displays graphically quantitative data.
This function wraps the matplotlib area function.

Parameters
----------
x : label or position, optional
    Coordinates for X point.
y : label or position, optional
    Coordinates for Y point.
kwds : optional
    Keyword arguments to pass on to :py:meth:`pandas.DataFrame.plot`.

Returns
-------
matplotlib.AxesSubplot or numpy.ndarray
    Area plot generated.

See Also
--------
pandas.DataFrame.plot : Draw a plot using matplotlib.

Examples
--------
.. plot::
    :context: close-figs

    This example draws an area plot based on the length and width of
    some animals, displayed in three bins

    >>> df = pd.DataFrame({
    ...     'sales': [3, 2, 3, 9, 10, 6],
    ...     'visits': [20, 42, 28, 62, 81, 50],
    ... })
    >>> area = df.plot.area()

################################################################################
################################## Validation ##################################
################################################################################

Docstring for "pandas.DataFrame.plot.area" correct. :)
```
