Fix #2316: handle absent Promise for better IE11 support

[muodov]

Purpose (TL;DR) - mandatory

Fix #2316: Don't raise exceptions if Promise is not defined

How to verify - mandatory

1. Check out this branch
2. npm install
3. Use the library in IE11

Checklist for author

• npm run lint passes
• References to standard library functions are cached.

[fatso83]

Seems legit, but should probably test drive this in our Sauce labs suite.

[muodov]

@fatso83 Thanks for the review!
The test suite (as far as I can see), is doing a similar check itself, so those tests are just skipped.
I tested it manually in our product (where it broke in the first place), and the fix worked there.
Please let me know what I can do to get this merged soon.

[mantoni]

Tests are already skipped correctly when Promise is not defined. Thank you @muodov 👍

I can't make a release atm. If anyone else in @sinonjs/sinon-core could, that'd be great.

[mroderick]

This has been published as sinon@9.2.2