fix aexit for orderbook

Author: csko

gdax/orderbook.py

@@ -93,11 +93,11 @@ async def __aenter__(self):
         return self
 
     async def __aexit__(self, exc_type, exc, traceback):
-        tasks = [self._ws_session.__aexit__(exc_type, exc, traceback)]
-        if self.trade_log_file_path is not None:
-            tasks.append(self._close_log_file())
-        res = await asyncio.gather(*tasks)
-        return tasks[0]
+        res = await asyncio.gather(
+            self._ws_session.__aexit__(exc_type, exc, traceback),
+            self._close_log_file(),
+        )
+        return res[0]
 
     async def _open_log_file(self):
         if self.trade_log_file_path is not None: