Add webpack option

[dflupu]

Fixes #143

[sindresorhus]

Sorry for the super slow review. I'm finally getting through all my PRs now.

[sindresorhus]

You're testing that the config is correctly handled, but I think this needs an integration test too that ensures it actually works in practice in a Webpack project.

[dflupu]

You're testing that the config is correctly handled, but I think this needs an integration test too that ensures it actually works in practice in a Webpack project.

I'm not sure how that could be done without actually adding Webpack as a dev dependency.

[sindresorhus]

I'm not sure how that could be done without actually adding Webpack as a dev dependency.

We can add Webpack as a dev dependency.

[sindresorhus]

Looks good to me now. Thanks for working on it :)

[dflupu]

Thanks for the feedback on this! Felt like I've learned a few things.