`@import` doesn't work well with symlinks

[malash]

I created a reproduce demo here https://github.com/peerigon/extract-loader/pull/64/files

In this case the main.css imports common.css which is a symlink to symlinks/common.css.

      1 .
      2 ├── symlinks
      3 │   └── common.css -> ../common.css
      4 ├── common.css
      5 ├── hi.jpg
      6 ├── index.html
      7 ├── main.css
      8 └── main.js
      9
     10 1 directory, 6 files

The Webpack build failed because the basedir in resolve.sync was wrong.

https://github.com/peerigon/extract-loader/blob/c82150a30d72b977871ffc89e8db8ccb7e97a362/src/extractLoader.js#L101