feat: add typescript definitions

[ForbesLindesay]

No description provided.

[rollingversions]

Change Log for is-promise (2.2.2 → 3.0.0)

Breaking Changes

• This package now comes bundled with TypeScript definitions

  This means you may get new errors that you didn't see before if you are using TypeScript. If you are not using TypeScript, this change will not impact you.

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[ForbesLindesay]

@mvila would you be able to give this a quick look to sanity check what I've done? As with all these small libraries, it feels like 90% of the work is writing the tests.

[LarryBattle]

Even though it might be redundant, could you add a test for Promise.resolve()?

assert(isPromise(Promise.resolve()) === true);

[mvila]

Thanks, @ForbesLindesay! It all sounds good to me.