[RegExp] Match Indices

[uufc]

execute:
const test = new RegExp('.', 'd');
output:
Uncaught SyntaxError: Invalid flags supplied to RegExp constructor 'd'
at new RegExp ()
at :1:14
(anonymous) @ VM524:1

---

https://github.com/tc39/proposal-regexp-match-indices

[zloirock]

Feel free to add a PR.