Dpo vocab size clarification (#628)

* Llama3 from scratch improvements

* vocab size should be 50257 not 50256

* restore

ch07/04_preference-tuning-with-dpo/dpo-from-scratch.ipynb

@@ -2140,7 +2140,7 @@
    },
    "source": [
     "- In other words, `torch.gather` is a selection function\n",
-    "- When we computed the loss earlier, we used it to retrieve the log probabilities corresponding to the correct token in the 50,256-token vocabulary\n",
+    "- When we computed the loss earlier, we used it to retrieve the log probabilities corresponding to the correct token in the 50,257-token vocabulary\n",
     "- The \"correct\" tokens are the tokens given in the response entry"
    ]
   },
@@ -3112,7 +3112,7 @@
    "provenance": []
   },
   "kernelspec": {
-   "display_name": ".venv",
+   "display_name": "Python 3 (ipykernel)",
    "language": "python",
    "name": "python3"
   },
@@ -3126,7 +3126,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.12.6"
+   "version": "3.10.16"
   }
  },
  "nbformat": 4,