Remove telegram deprecation warning

closes #4688

freqtrade/rpc/telegram.py

@@ -159,10 +159,10 @@ class Telegram(RPCHandler):
         for handle in handles:
             self._updater.dispatcher.add_handler(handle)
         self._updater.start_polling(
-            clean=True,
             bootstrap_retries=-1,
             timeout=30,
             read_latency=60,
+            drop_pending_updates=True,
         )
         logger.info(
             'rpc.telegram is listening for following commands: %s',

setup.py

@@ -69,7 +69,7 @@ setup(name='freqtrade',
           # from requirements.txt
           'ccxt>=1.24.96',
           'SQLAlchemy',
-          'python-telegram-bot',
+          'python-telegram-bot>=13.4',
           'arrow>=0.17.0',
           'cachetools',
           'requests',