Fixes #243 honoring mutable cache ttl-ness in getOrElseUpdate and hit

So, the intent of hit is that it is refreshing the cache. If you don't want to refresh the cache and keep the key hot, you use get.

I think you want a slightly different behavior actually. You want a TTL that expires from the first entry, no matter what.

Should we make a different class to address this, or is the current use case totally unreasonable?