DOC: Fix Malformed table. Text in column margin

Sphinx 1.2.2 on Windows throws the following error:
```
ERROR: Malformed table. Text in column margin in table line 22.

==========  ==========================================================
Argument    Description
==========  ==========================================================
*xs*, *ys*  Positions of data points.
*zs*        Either an array of the same length as *xs* and
            *ys* or a single value to place all points in
            the same plane. Default is 0.
*zdir*      Which direction to use as z ('x', 'y' or 'z')
            when plotting a 2D set.
*s*         size in points^2.  It is a scalar or an array of the same
            length as *x* and *y*.

*c*         a color. *c* can be a single color format string, or a
            sequence of color specifications of length *N*, or a
            sequence of *N* numbers to be mapped to colors using the
            *cmap* and *norm* specified via kwargs (see below). Note
            that *c* should not be a single numeric RGB or RGBA
            sequence because that is indistinguishable from an array
            of values to be colormapped.  *c* can be a 2-D array in
            which the rows are RGB or RGBA, however.

*depthshade*
            Whether or not to shade the scatter markers to give the
            appearance of depth. Default is *True*.
==========  ==========================================================
```