gTTSでmp3保存できません

Question

前提・実現したいこと

gTTSで日本語を読み上げさせた音声を保存したいのですがエラーが起きます。

発生している問題・エラーメッセージ

--------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-24-daa5fb84901f> in <module>
      6 filename = r'C:\Users\sern3\Desktop\petgazou\voice\mugi.mp3' #mp3ファイル
      7 
----> 8 tts.save(filename)

c:\users\sern3\appdata\local\programs\python\python36\lib\site-packages\gtts\tts.py in save(self, savefile)
    293                             # no audio stream in response
    294                             raise gTTSError(tts=self, response=r)
--> 295                 log.debug("part-%i written to %s", idx, fp)
    296             except (AttributeError, TypeError) as e:
    297                 raise TypeError(

c:\users\sern3\appdata\local\programs\python\python36\lib\site-packages\gtts\tts.py in write_to_fp(self, fp)
    249         Raises:
    250             :class:`gTTSError`: When there's an error with the API request.
--> 251             TypeError: When ``fp`` is not a file-like object that takes bytes.
    252 
    253         """

c:\users\sern3\appdata\local\programs\python\python36\lib\site-packages\gtts\tts.py in _prepare_requests(self)
    192 
    193         text_parts = self._tokenize(self.text)
--> 194         log.debug("text_parts: %s", str(text_parts))
    195         log.debug("text_parts: %i", len(text_parts))
    196         assert text_parts, 'No text to send to TTS API'

c:\users\sern3\appdata\local\programs\python\python36\lib\site-packages\gtts_token\gtts_token.py in calculate_token(self, text, seed)
     26 
     27 
---> 28     def calculate_token(self, text, seed=None):
     29         """ Calculate the request token (`tk`) of a string
     30         :param text: str The text to calculate a token for

c:\users\sern3\appdata\local\programs\python\python36\lib\site-packages\gtts_token\gtts_token.py in _get_token_key(self)
     57         a %= 1E6
     58         a = int(a)
---> 59         return str(a) + "." + str(a ^ int(first_seed))
     60 
     61     def _get_token_key(self, retry=0):

ValueError: Unable to find token seed! Did https://translate.google.com change?

該当のソースコード

from gtts import gTTS

mytext = "これは麦茶です"
tts = gTTS(text=mytext, lang='ja')

filename = r'C:\Users\sern3\Desktop\petgazou\voice\mugi.mp3' #mp3ファイル

tts.save(filename)