Update import to nested path (#109)

* Update import to nested path

* Update python_coreml_stable_diffusion/unet.py

Co-authored-by: Pedro Cuenca <pedro@huggingface.co>

Co-authored-by: Atila Orhon <64497909+atiorh@users.noreply.github.com>
Co-authored-by: Pedro Cuenca <pedro@huggingface.co>

python_coreml_stable_diffusion/unet.py

@@ -6,7 +6,7 @@
 from python_coreml_stable_diffusion.layer_norm import LayerNormANE
 
 from diffusers.configuration_utils import ConfigMixin, register_to_config
-from diffusers.modeling_utils import ModelMixin
+from diffusers import ModelMixin
 
 from enum import Enum