module.exports = function sequential() {
  if (this.busy || this.limited || this.queue.length === 0) return;
  this.busy = true;
  this.execute(this.queue.shift())
    .then(() => {
      this.busy = false;
      this.handle();
    })
    .catch(({ timeout }) => {
      if (timeout) {
        this.client.setTimeout(() => {
          this.reset();
          this.busy = false;
          this.handle();
        }, timeout);
      }
    });
};