Cuando ejecute el siguiente código

 from gtts import gTTS
 tts = gTTS('hello')
 tts.save('hello.mp3')

Obtengo "AttributeError: el objeto 'NoneType' no tiene ningún atributo 'group'".

Traceback (most recent call last):

File "C:\Users\HP\Desktop\Desktop\programming\Python_code\New Text Document - Copy (8) - Copy.py", line 3, in <module>
    tts.save('hello.mp3')
  File "C:\Users\HP\AppData\Local\Programs\Python\Python36\lib\site-packages\gtts\tts.py", line 247, in save
    self.write_to_fp(f)
  File "C:\Users\HP\AppData\Local\Programs\Python\Python36\lib\site-packages\gtts\tts.py", line 187, in write_to_fp
    part_tk = self.token.calculate_token(part)
  File "C:\Users\HP\AppData\Local\Programs\Python\Python36\lib\site-packages\gtts_token\gtts_token.py", line 28, in calculate_token
    seed = self._get_token_key()
  File "C:\Users\HP\AppData\Local\Programs\Python\Python36\lib\site-packages\gtts_token\gtts_token.py", line 62, in _get_token_key
    a = re.search("a\\\\x3d(-?\d+);", tkk_expr).group(1)
AttributeError: 'NoneType' object has no attribute 'group'

¿Es posible usar gTTS en Python?