Add typing_extensions to make it work in Python 3.7

main.py

@@ -8,7 +8,12 @@ from datetime import date, datetime, timedelta
 from itertools import groupby
 from pprint import pformat
 from textwrap import dedent
-from typing import Dict, Literal, Optional, Set
+from typing import Dict, Optional, Set
+
+try:
+    from typing import Literal
+except ImportError:
+    from typing_extensions import Literal  # type: ignore
 
 from dotenv import load_dotenv
 from telegram import InlineKeyboardButton, InlineKeyboardMarkup, Update