function _expandUnicodeEscapes(s) {
  return s.replace(/\\([0-9a-f]{1,6})\s/gi, function() {
    let code = arguments[1],
      repeat = 6 - code.length;
    while (repeat--) {
      code = '0' + code;
    }
    return '\\' + code;
  });
}
conversion of sort unicode escapes with spaces like `\33 ` (and longer) into
expanded form that doesn't require trailing space `\000033`
@param {string} s
@return {string}