Wrong DICE calculate in evaluate.py

[umeiko]

As titled, When I trained my multiclass tasks, i found Dice Score were too high, which is abnormal. then I found calculation of Dice were wrong.

in evaluate.py, line 37:

dice_score += multiclass_dice_coeff(mask_pred[:, 1:], mask_true[:, 1:], reduce_batch_first=False)

which should be:

dice_score += multiclass_dice_coeff(mask_pred[:, 1:], mask_true[:, 1:], reduce_batch_first=True)