Update train_ddp.py

train_ddp.py

-
 from __future__ import print_function
 from __future__ import division
 
@@ -48,7 +47,7 @@ parser.add_argument('--adadelta', action='store_true', help='Whether to use adad
 parser.add_argument('--keep_ratio', action='store_true', help='whether to keep ratio for image resize')
 parser.add_argument('--manualSeed', type=int, default=1234, help='reproduce experiemnt')
 parser.add_argument('--random_sample', action='store_true', help='whether to sample the dataset with random sampler')
-parser.add_argument('--local_rank', type=int, default=1, help='local rank environ')
+parser.add_argument('--local-rank', type=int, default=1, help='local rank environ')
 parser.add_argument('--world-size', default=4, type=int, help='number of distributed processes')
 opt = parser.parse_args()
 print(opt)