shouldThrow should use exception class hierarchy instead of exact class

[neyb]

{ throw IllegalStateException() } shouldThrow RuntimeException::class should pass

[MarkusAmshove]

(for the record)
I've tested what JUnits behavior would be in this case.

This test passes:
@Test(expected = RuntimeException.class) public void test() { new ArrayList<>().get(0); }

So the Exceptionhierarchy is expected behavior

[MarkusAmshove]

I merged your PR into master and released both changes into 1.9.

Thanks for your contribution!