Revert sleep time to 1.1 from 2.0 (#41)

Apparently there's a hardcoded value of `1.2` in https://github.com/faust-streaming/mode/blob/17c5d2996e4706baa37b18bd8fa03687409120ad/mode/timers.py#L13 so we may have made a terrible mistake.

mode/threads.py

@@ -181,7 +181,7 @@ async def start(self) -> None:
 
     async def _keepalive2(self) -> None:
         while not self.should_stop:
-            await self.sleep(2.0)
+            await self.sleep(1.1)
             if self.last_wakeup_at:
                 if monotonic() - self.last_wakeup_at > 3.0:
                     self.log.error("Thread keepalive is not responding...")