Update purge options

[borisdayma]

As an alternative, it could be written with the object syntax:

module.exports = {
  purge: {
    content: ['./src/**/*.html'],
  },
  // ...
}

What is important is to have purge section for it to work in prod mode (dev does not use purge by default).

[acidjazz]

got it thanks! I'll add it from a commit