fix: use virtualNode in title-only check

[marcysutton]

Closes #388

[marcysutton]

Passing tests for title-only:

title-only
    ✓ should return true if an element only has a title
    ✓ should return true if an element only has aria-describedby

[WilcoFiers]

@marcysutton @dylanb Shouldn't we add shadow DOM tests for these rules?

[dylanb]

@WilcoFiers I thought about that and I came to the conclusion that we do not need tests for every rule - however I may be wrong... here is my thinking...

If the utility functions work properly (i.e. they are tested properly) and if the rule has a good level of tests for all of its edge cases, then adding shadow DOM tests does not add more quality unless the rule has some specific functionality itself that pertains to shadow DOM.

This does not mean that we cannot add shadow DOM tests, it just means we don't necessarily need them - thoughts?