Update clean-webpack-plugin and include as default for production builds.

[mattheu]

It would be nice to include clean-webpack-plugin for production builds to ensure the build directory doesn't contain any old files.

Let me know your thoughts - happy to open a PR for this.

[mattheu]

Such an idiot - didn't see this was bundled.

However - the version bundled is 1.0, but the plugin is now at 3.0. The latest version doesn't require you to pass paths, if you just call new CleanPlugin() then it automatically cleans the webpack output path - zero config required. So currently its less config to just use the plugin directly and skip the webpack-helpers version.

Additionally... any reason not to just clean the webpack output path by default for production builds?

[kadamwhite]

No strong opinions on cleaning by default, I think if I consider your argument for long enough you'll have me convinced. We should definitely update the dependency, nice catch.

[kadamwhite]

We cannot actually clean by default, because then if somebody does

module.exports = [
  presets.production( { ... } ),
  presets.production( { ... } ),
];

then only one build will get output correctly (whichever runs second will clear the build folder, removing all files from the first-run build). However, this can be added as an option, for sure.