code: func (q *EvictingStringQueue) Peek() string {
  	q.mu.Lock()
  	l := len(q.vals)
  	if l == 0 {
  		q.mu.Unlock()
  		return ""
  	}
  	elem := q.vals[l-1]
  	q.mu.Unlock()
  	return elem
  }
docs: // Peek looks at the last element added to the queue.