in app/build/utils.js [64:74]
    stylus: generateLoaders('stylus'),
    styl: generateLoaders('stylus')
  }
}
// Generate loaders for standalone style files (outside of .vue)
exports.styleLoaders = function (options) {
  const output = []
  const loaders = exports.cssLoaders(options)
  for (const extension in loaders) {