Fix NaN detection in .is()

[panva]

NaN is not a number, this fixes the is() return for it.

before

is(NaN) // => 'number'

after

is(NaN) // => 'NaN'

---

Fixes #160

[panva]

I think this doesn't have to be considered a breaking but will leave that up to you @sindresorhus.

[sindresorhus]

The PR looks good, but since I'm planning a major release here in a month or two, I'm gonna keep this PR open until such time, as I don't see the point in risking it breaking for someone.

[sindresorhus]

Tests are failing.

[panva]

Number.isNaN is not defined to only take an argument of type number.

I can either // @ts-ignore this , put it back to the number switch case it was at originally, or cast to <number> to satisfy this broken type definition.

[sindresorhus]

put it back to the number switch case it was at originally

I guess this is the easiest then. Sorry for the back and forth.

[sindresorhus]

Finally out: https://github.com/sindresorhus/is/releases/tag/v5.0.0