More Findbugs reports <3

Syncing on a Boolean object, which is globally shared, and not implementing hashCode() for something you use as a hashmap key.
Evidence: https://github.com/MassiveCraft/mcore/blob/fe6ce0103794950835fc10be2ec9e1153b6860a0/src/com/massivecraft/mcore/util/TimeDiffUtil.java#L73