Fix wrong call to the underlying method when checking if an object is frozen

[astorije]

No description provided.

[keithamus]

Ooops, good call. Missed that in the PR. Thanks @astorije

[astorije]

For the record, here is why this buggy version passes the tests:

> var v = { foo: "bar" }
undefined
> Object.isSealed(v)
false
> Object.isFrozen(v)
false
> Object.freeze(v)
{ foo: 'bar' }
> Object.isSealed(v)
true
> Object.isFrozen(v)
true

So if you are frozen, you are sealed.

(Note that the opposite is not true:

> var v2 = { foo: "bar" }
undefined
> Object.isSealed(v2)
false
> Object.isFrozen(v2)
false
> Object.seal(v2)
{ foo: 'bar' }
> Object.isSealed(v2)
true
> Object.isFrozen(v2)
false

)

[astorije]

@keithamus, can you quickly release version 3.1.1 to make sure anyone who gladly switched to version 3.1.x to have these methods does not fall in this bug?