add missing util require

index.js

@@ -5,6 +5,7 @@ const thunky = require('thunky')
 const debug = require('debug')('cobox-blind-replicator')
 const pump = require('pump')
 const hyperswarm = require('hyperswarm')
+const util = require('util')
 
 module.exports = (storage, address, opts = {}) => (
   new BlindReplicator(storage, address, opts)