document.createElement('dialog') should not return HTMLElement as type

[Akxe]

TypeScript Version: 2.9.2, 3.0.1

Search Terms:
createElement dialog
Code

const dialog: HTMLDialogElement = document.createElement('dialog');

Expected behavior:
No error...

Actual behavior:
Type 'HTMLElement' is not assignable to type 'HTMLDialogElement'.

Playground Link:
http://www.typescriptlang.org/play/#src=const%20dialog%3A%20HTMLDialogElement%20%3D%20document.createElement('dialog')%3B

Related Issues:
Few about adding dialog element definition.

[mhegazy]

PRs welcomed. You can find more information about contributing lib.d.ts fixes at https://github.com/Microsoft/TypeScript/blob/master/CONTRIBUTING.md#contributing-libdts-fixes.

[AbhiPrasad]

First time peeking around lib files, figured I would give it a hand. Opened up a PR to fix this (linked above)!