code: function (source, destination) {
      return cont.mapAsync(readFileAsJSON(source), function (json, cb) {
          json.copied = Date.now()
          fs.writeFile(destination, JSON.stringify(json), cb)
      })
  }
docs: mapAsync takes an asynchronous transformation function and a source continuable. The new continuable is the value of the first continuable passed through the async transformation.