fix py37 syntax

Author: blink1073

jupyter_client/kernelspecapp.py

@@ -4,6 +4,7 @@
 import json
 import os.path
 import sys
+import typing as t
 
 from jupyter_core.application import base_aliases
 from jupyter_core.application import base_flags
@@ -309,8 +310,8 @@ class KernelSpecApp(Application):
         }
     )
 
-    aliases: dict[str, object] = {}
-    flags: dict[str, object] = {}
+    aliases: t.Dict[str, object] = {}
+    flags: t.Dict[str, object] = {}
 
     def start(self):
         if self.subapp is None: