Add missing dilation in mask_rcnn_fcn_head

Summary:
Dilation value `cfg.MRCNN.DILATION` is only used to calculate padding for conv, but not assigned to the dilation argument of conv.
Closes https://github.com/facebookresearch/Detectron/pull/388

Reviewed By: rbgirshick

Differential Revision: D8160945

Pulled By: ir413

fbshipit-source-id: dca6a5cf7659f29a5d1d91e860c9dfff4963e7c3

detectron/modeling/mask_rcnn_heads.py

@@ -153,6 +153,7 @@ def mask_rcnn_fcn_head_v1upXconvs(
             dim_in,
             dim_inner,
             kernel=3,
+            dilation=dilation,
             pad=1 * dilation,
             stride=1,
             weight_init=(cfg.MRCNN.CONV_INIT, {'std': 0.001}),