Unmet peer dependency with Webpack 4

[nickensoul]

In my case, loader works fine with Webpack 4, but throws unmet peer dep.
Console output using command npm list -depth=0:

├── ...
├── UNMET PEER DEPENDENCY webpack@4.28.1

npm ERR! peer dep missing: webpack@^3 || ^2 || ^2.2.0-rc.0 || ^2.1.0-beta || ^1.12.6, required by sass-extract-loader@1.1.0

My suggestion is to add Webpack 4 version to peers, if loader works as expected with this version.
Thanks.

[kenime]

I am happy to create a PR for this, but since webpack 4 requires node version >= 6.11.5 (current package requirement is >=4), technically this is a breaking change.

@jgranstrom need your advice in whether to bump a major version or minor version.

[DanielSchaffer]

@kenime I'm obviously not the maintainer, but I'd recommend a major version - that way folks on older versions of node using a ^ semver pattern don't get hosed.