return then-callback promise

[tunnckoCore]

Like that on L48-49-50

promise = utils.normalizePromise(resolved, promise)
return utils.then(promise)

to be even able to pass callback to the returned promise's .then method.

const fs = require('fs')
const hybridify = require('hybridify')
const readdir = hybridify.hybridify(fs.readdir)

// called two times
function callback (err, files) {
  if (err) return console.error('callback err:', err)
  console.log('callback res:', files) // => array with directory files
}

const promise = readdir('./', callback)
promise.then(callback)