fix timm version compatibility (#331)

* Fix timm version compatibility

easycv/models/backbones/efficientformer.py

@@ -1,15 +1,21 @@
 # Copyright (c) 2022 Snap Inc. All rights reserved.
 import itertools
 import os
+from distutils.version import LooseVersion
 
+import timm
 import torch
 import torch.nn as nn
 from timm.models.layers import DropPath, trunc_normal_
-from timm.models.layers.helpers import to_2tuple
 
 from ..modelzoo import efficientformer as model_urls
 from ..registry import BACKBONES
 
+if LooseVersion(timm.__version__) <= LooseVersion('0.8.2'):
+    from timm.models.layers.helpers import to_2tuple
+else:
+    from timm.layers.helpers import to_2tuple
+
 
 class Attention(torch.nn.Module):