Fix size compatibility for model.forward

Error was coming from "modeling_pytorch.py", line 484, in forward: start_loss = loss_fct(start_logits, start_positions) --> ValueError: Expected target size (12, 1), got torch.Size([12])

run_squad_pytorch.py

@@ -840,6 +840,9 @@ def main():
                 #label_ids = label_ids.to(device)
                 start_positions = start_positions.to(device)
                 end_positions = start_positions.to(device)
+                
+                start_positions = start_positions.view(-1, 1)
+                end_positions = end_positions.view(-1, 1)
 
                 loss, _ = model(input_ids, segment_ids, input_mask, start_positions, end_positions)
                 loss.backward()