Trac #18406: Fix times in graphics doc

The docstring for `show` is raw (`r""" ... """`)
and contains
{{{
`[0,1]\\times[0,1]`
}}}
which does not render right in the
[http://www.sagemath.org/doc/reference/plotting/sage/plot/graphics.html#
sage.plot.graphics.Graphics.show show documentation].

In a raw string, `\\times` becomes `\\` (newline) + `times`.

The fix is to use `\times` instead of `\\times`.

URL: https://trac.sagemath.org/18406
Reported by: kcrisman
Ticket author(s): Samuel Lelièvre
Reviewer(s): Karl-Dieter Crisman

src/sage/plot/graphics.py

@@ -1626,7 +1626,7 @@ def show(self, **kwds):
             ``(x_pos, y_pos)`` which indicate the relative position of the
             title within the plot. The plot itself can be considered to
             occupy, in relative terms, the region within a unit square
-            `[0,1]\\times[0,1]`.  The title text is centered around the
+            `[0, 1] \times [0, 1]`.  The title text is centered around the
             horizontal factor ``x_pos`` of the plot. The baseline of the
             title text is present at the vertical factor ``y_pos`` of the
             plot. Hence, ``title_pos=(0.5, 0.5)`` will center the title in