fix example for 3.8

example/client.py

@@ -1,13 +1,22 @@
 import asyncio
+import sys
 
 from example.events import Message
 from socketapp import Client
 
+if sys.version_info < (3, 9, 0):
+    from concurrent.futures import ThreadPoolExecutor
+
 
 async def send(client: Client) -> None:
     await client.wait_until_ready()
     while True:
-        inp = await asyncio.to_thread(input)
+        if sys.version_info < (3, 9, 0):
+            with ThreadPoolExecutor(1, "AsyncInput") as executor:
+                inp = await asyncio.get_event_loop().run_in_executor(executor, input)
+        else:
+            inp = await asyncio.to_thread(input)
+
         await client.send(Message(data=inp), client.clients)