fix flake8

tools/train.py

@@ -14,7 +14,8 @@ def parse_args():
     parser = argparse.ArgumentParser(description='Train a detector')
     parser.add_argument('config', help='train config file path')
     parser.add_argument('--work_dir', help='the dir to save logs and models')
-    parser.add_argument('--resume_from', help='the checkpoint file to resume from')
+    parser.add_argument(
+        '--resume_from', help='the checkpoint file to resume from')
     parser.add_argument(
         '--validate',
         action='store_true',