sourcemaps sources will include "\" on windows

[kyaido]

mozilla/source-map#91

See the above issue, sourcemaps sources will include \ on windows.
In index.js#L77, would not it should be considered in the case of \?

[kyaido]

This is sample .map file that created by same sample project files.

On windows

{"version":3,"sources":["_module.scss","C:/sourcemap-sandbox/src/scss/main.scss"],"names":[],"mappings":"...","file":"main.css","sourceRoot":"../../src/scss"}

On Mac

{"version":3,"sources":["_module.scss","main.scss"],"names":[],"mappings":"...","file":"main.css","sourceRoot":"../../src/scss"}

[kyaido]

This issue was resolved by #314.
Thanks!