old_contents: module.exports = (ctx) => ({
      plugins: {
          'postcss-import': { root: ctx.file.dirname },
          'postcss-cssnext': {},
          'postcss-discard-comments': { removeAll: true },
          'cssnano': ctx.env === 'production' ? {} : false
      }
  })
  
new_contents: module.exports = (ctx) => ({
      plugins: {
          'postcss-import': { root: ctx.file.dirname },
          'postcss-nested': {},
          'postcss-cssnext': {},
          'postcss-discard-comments': { removeAll: true },
          'cssnano': ctx.env === 'production' ? {} : false
      }
  })
  
subject: Add postcss-nested plugin to config