path.relative doesn't work as expected

[colynb]

When passing file paths to path.relative it generates a path that I wouldn't expect. Better to use just the dirname of the file instead.

If I have a generated folder:

dist
 -- img
   -- sprite.png
 -- css
   -- sprite.css

I would expect the image path to be ../img/sprite.png and not ../../img/sprite.png which is what is happening now.

[Otouto]

Hi. I`ve refactored plugin, so now it more fits gulp style. Please, check if it works for you ok in version 0.0.2.