template don't accept absolute paths

[Congelli501]

I went from css-sprite@0.9.8 to sprity@1.0.7, and with the new version absolute path to the mustache template don't work anymore.

If I use:
{
template: '/absolute/path/category.less.template'
}

Then, sprity tries to find the template in `/absolute/path/category.less.template', and the build fails.

If the path begins with a "/", then the cwd should not be prepended to the path.