Update requirements.txt

It seems there's an issue with python_telegram_bot v12.8 that causes import errors with the telegram package.
Other instances of this issue cropping up are:
python-telegram-bot/python-telegram-bot#395
Tkd-Alex/Telegram-InstaPy-Scheduling#13
python-telegram-bot/python-telegram-bot#1670
https://stackoverflow.com/questions/59446910/importerror-cannot-import-name-type-python-telegram-bot
https://stackoverflow.com/questions/58067952/importerror-cannot-import-name-message-from-exchangelib-folders
python-telegram-bot/python-telegram-bot#1223


The working solution seems to be upgrading to v13.0

requirements.txt

@@ -1,5 +1,5 @@
 pymongo==3.11.0
 requests==2.24.0
-python_telegram_bot==12.8
+python_telegram_bot==13.0
 beautifulsoup4==4.9.2
 telegram==0.0.1