Change yield to sleep(0)

Per @dhalbert's recommendation

Author: tekktrik

asyncio/event.py

@@ -58,7 +58,7 @@ async def wait(self):
             self.waiting.push_head(core.cur_task)
             # Set calling task's data to the event's queue so it can be removed if needed
             core.cur_task.data = self.waiting
-            yield
+            core.sleep(0)
         return True