Webpack watchOptions not passed to compiler in watch mode
Motivation was to ignore node_modules from `skpm build --watch` as it was caning CPU on my system.

webpack.config supports `watchOptions` option, but this is poorly documented and appears to apply only to webpack-dev-server, not compiler instances.

`compiler.watch()` takes `watchOptions` as the first argument, but in skpm/builder this was specified as an empty object.

Solution is to take `watchOptions` from `compiler.options` and pass them to `compiler.watch()`.

Discusion: https://github.com/webpack/webpack.js.org/issues/125