Update Trio mode for compatibility with Trio >= 0.18.0

The Trio package renamed their trio.hazmat module to trio.lowlevel.

Author: mehaase

ipykernel/trio_runner.py

@@ -39,7 +39,7 @@ def log_nursery_exc(exc):
                 exc)
 
         async def trio_main():
-            self._trio_token = trio.hazmat.current_trio_token()
+            self._trio_token = trio.lowlevel.current_trio_token()
             async with trio.open_nursery() as nursery:
                 # TODO This hack prevents the nursery from cancelling all child
                 # tasks when an uncaught exception occurs, but it's ugly.