(trivial) fix some import orders

1. stdlib
2. 3rd-party
3. internal

(as in PEP-8)

electrum/lnrouter.py

@@ -29,9 +29,10 @@ from typing import Sequence, Tuple, Optional, Dict, TYPE_CHECKING, Set
 import time
 import threading
 from threading import RLock
-import attr
 from math import inf
 
+import attr
+
 from .util import profiler, with_lock
 from .logging import Logger
 from .lnutil import (NUM_MAX_EDGES_IN_PAYMENT_PATH, ShortChannelID, LnFeatures,