client: update comment

See commit 8ef1ddba.

neo/client/transactions.py

@@ -120,7 +120,7 @@ class Transaction(object):
                 assert lockless < serial, (lockless, serial)
                 uuid_list.append(uuid)
                 return
-            # It's safe to do this after the above excepts: either the cell is
+            # It's safe to do this after the above except: either the cell is
             # already marked as lockless or the node will be reported as failed.
             lockless = self.lockless_dict
             if not lockless: