add from __future__ import annotations for Python 3.8

Author: limwz01

ipykernel/_version.py

@@ -1,6 +1,8 @@
 """
 store the current version info of the server.
 """
+from __future__ import annotations
+
 import re
 
 # Version string must appear intact for hatch versioning

ipykernel/inprocess/channels.py

@@ -2,6 +2,7 @@
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
+from __future__ import annotations
 
 from jupyter_client.channelsabc import HBChannelABC
 

ipykernel/pickleutil.py

@@ -2,6 +2,8 @@
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
+from __future__ import annotations
+
 import copy
 import pickle
 import sys

ipykernel/thread.py

@@ -1,4 +1,6 @@
 """Base class for threads."""
+from __future__ import annotations
+
 import typing as t
 from threading import Event, Thread