input: Write a python function to find and return duplicates in a text.
  assert find_duplicates("programming")==['r', 'g', 'm']
  assert find_duplicates("hello")==['l']
  assert find_duplicates("test")==['t']
output: def find_duplicates(text):
      from collections import Counter
      counter = Counter(text)
      return [char for char, count in counter.items() if count > 1]