Resolve will be performed for v6 even if there's a cache entry for v4

Every time lookup() is called it will result in a resolve() call for v6 even if there are cached results for v4. Ideally I'd like it so that if there's something in the cache for v4 OR v6 then it doesn't do any resolve() calls. I'm unsure if this is intentional or just a side effect of the fact that the cache reads are done in parallel.

WDYT?

I can work on a PR to change this if you agree.