Python3.8 support. Ref https://github.com/GNS3/gns3-gui/issues/2895

gns3server/utils/asyncio/__init__.py

@@ -22,8 +22,6 @@ import sys
 import os
 import threading
 
-from asyncio.futures import CancelledError
-
 
 async def wait_run_in_executor(func, *args, **kwargs):
     """
@@ -56,7 +54,7 @@ async def cancellable_wait_run_in_executor(func, *args, **kwargs):
     kwargs['stopped_event'] = stopped_event
     try:
         await wait_run_in_executor(func, *args, **kwargs)
-    except CancelledError:
+    except asyncio.CancelledError:
         stopped_event.set()