Relative import for roi_align (#4533)

Author: NicolasHug

torchvision/ops/poolers.py

@@ -2,7 +2,7 @@
 from torch import nn, Tensor
 
 import torchvision
-from torchvision.ops import roi_align
+from .roi_align import roi_align
 from torchvision.ops.boxes import box_area
 
 from typing import Optional, List, Dict, Tuple, Union