fix left side of shadow/item in tasks svg

good news everyone!! from what i can tell the annoying vertical lines,
as well as mismatching gradients in the tasks svgz's are all fixed now.
the Real Fix would be to make them vector, they shouldn't be raster, and
i'm sure it can be avoided/fixed. but i'm a hacker, not so much an
artist ;)
(cherry picked from commit 434300c06bd28993d41a8a7036b896bbfa3578a3)

M +- -- desktoptheme/air/widgets/tasks.svgz