Fix typo in prompt-tuning-sst2.ipynb (#245)

examples/prompt-tuning-sst2.ipynb

@@ -399,7 +399,7 @@
     "    head_layer_position=HEAD_LAYER_POSITION,\n",
     ")\n",
     "cls_optimizer = AdamW(cls_model.parameters(), lr=LR, weight_decay=WEIGHT_DECAY)\n",
-    "cls_criterion = nn.CrossEntoryCriterion()\n",
+    "cls_criterion = nn.CrossEntropyCriterion()\n",
     "\n",
     "lr_scheduler = get_scheduler(\n",
     "    name=\"linear\", optimizer=cls_optimizer, num_warmup_steps=0, num_training_steps=len(train_dataloader)\n",