Fix checking bitfield to use bitfield on replicator

Author: lejeunerenard

lib/prefetcher.js

@@ -46,7 +46,7 @@ module.exports = class Prefetcher {
     let end = this.end
 
     while (end < this.endBound && this.missing < this.max) {
-      end = this.core.core.bitfield.firstUnset(end) + 1
+      end = this.core.core.replicator.localBitfield.firstUnset(end) + 1
       if (end >= this.endBound) break
       this.missing++
     }