Usage of "~" sign in imports

[siarheiyelin]

According to https://github.com/webpack-contrib/sass-loader#imports the "~" sign is deprecated in "style-loader". If "~" isn't specified, then it tries to resolve it as a relative path first. If it cannot be resolved, then the loader will try to resolve @import inside "node_modules".

It would be useful to support same logic for imports as implemented in "style-loader". i.e. look into "node_modules" even if "~" is not added. So that both ways to import files are supported:

1. @import "~bootstrap/dist/css/bootstrap";
2. @import "bootstrap/dist/css/bootstrap";