feat: add prettify option

[sodatea]

closes #1426

[S1019269]

Can you provide an example configuration for vue-loader containing the prettify: false option? For me it is not taking effect.

[sodatea]

@S1019269

const VueLoaderPlugin = require('vue-loader/lib/plugin')

module.exports = {
  mode: 'development',
  devtool: false,
  output: {
    path: '/',
    filename: 'test.build.js'
  },
  module: {
    rules: [
      {
        test: /\.vue$/,
        loader: 'vue-loader',
        options: { prettify: false }
      },
      {
        test: /\.css$/,
        use: [
          'vue-style-loader',
          'css-loader'
        ]
      }
    ]
  },
  plugins: [
    new VueLoaderPlugin(),
    new webpack.optimize.ModuleConcatenationPlugin()
  ]
}