code: function pushPart (parts, file) {
    let ext = getExtname(file.path)
    let type = Object.keys(EXT_TYPES).find(key => {
      return EXT_TYPES[key].includes(ext)
    })
    parts[type.toLowerCase()].push(file)
  }
docs: Push peer file dependency into collected parts.
  @param {Object} parts Collected parts containing scripts and styles
  @param {Object} file The file to be appended