DinoDex refactor

Refactored DinoDex based on comments from first pull request.
you could technically shorten this with just `@dinosaurs.select { |dino| dino.name.to_s == dino_name }.pop.to_s` but that will only make this worse.

I think this is way too much work and probably reflects an opportunity to improve design somewhere else. Perhaps instead of an array of dinos, you could use a hash with names as keys.