Wrong Type declarations for .all() and .nextv() methods AbstractKeyIterator and AbstractValueIterator

[bredthau]

According to the typescript declarations the Promise overloads of .all() and .nextv() of AbstractKeyIterator return Promise<[K]>. However they should return a promise to an array of type K (so Promise<K[]> or Promise<Array<K>>). Similarly the Callback versions are declared to take NodeCallback<[K]> where it should be NodeCallback<Array<K>>.
The same situation exists for AbstractValueIterator, only with [V] where it should be Array<V> instead of [K].

[vweevers]

PR is welcome. Let's use the K[] notation rather than Array<K> (same as #67).