A parameter needs to be specified in unit 1 - 01_introduction_to_diffusers.ipynb

In this notebook, originally there is a line of code:
`image_pipe.save_pretrained("my_pipeline")`
, which will generate a saved model as 'diffusion_pytorch_model.safetensors'. However, it will cause errors in the following line
`pipeline = DDPMPipeline.from_pretrained(hub_model_id)`

After investigation, we have to specify one more parameter when saving model as follows,
`image_pipe.save_pretrained("my_pipeline", safe_serialization=False)`

Then, it should be work when loading our own trained model.