Fix typo in faster_rcnn.py

lib/model/faster_rcnn/faster_rcnn.py

@@ -49,7 +49,7 @@ class _fasterRCNN(nn.Module):
         # feed base feature map tp RPN to obtain rois
         rois, rpn_loss_cls, rpn_loss_bbox = self.RCNN_rpn(base_feat, im_info, gt_boxes, num_boxes)
 
-        # if it is training phrase, then use ground trubut bboxes for refining
+        # if it is training phase, then use ground truth bboxes for refining
         if self.training:
             roi_data = self.RCNN_proposal_target(rois, gt_boxes, num_boxes)
             rois, rois_label, rois_target, rois_inside_ws, rois_outside_ws = roi_data