Update es5.d.ts

[unional]

Objects.keys() does not take null or undefined

> Object.keys(undefined)
TypeError: Cannot convert undefined or null to object
> Object.keys(null)
TypeError: Cannot convert undefined or null to object

[x] You've signed the CLA
[x] There are new or updated unit tests validating the change

[houfio]

What about object?

[unional]

What about object?

object doesn't work with true and false

[ikatyang]

Related issue #17273

[rbuckton]

I think this looks like a good change, but would like to get some additional input. @sandersn, do you see any issues with this change?

[sandersn]

Looks good to me.