Update finetuning_llama3_8B_ptl_lora.rst

Update lightning version in docs to match the version is in the wget https://raw.githubusercontent.com/aws-neuron/neuronx-distributed/main/examples/training/llama/requirements_ptl.txt
 file.

Author: jimburtoft

libraries/neuronx-distributed/tutorials/finetuning_llama3_8B_ptl_lora.rst

@@ -54,7 +54,7 @@ We also download the requirements files for package dependencies and scripts to
 .. code:: ipython3
 
    python3 -m pip install -r requirements.txt
-   python3 -m pip install -r requirements_ptl.txt  # Currently we're supporting Lightning version 2.1.0
+   python3 -m pip install -r requirements_ptl.txt  # Currently we're supporting Lightning version 2.4.0
    chmod +x test_llama_lora_finetune.sh
    # prepare the dataset
    python3 -c "import nltk; nltk.download('punkt'); nltk.download('punkt_tab');"