New pip install doesn't align with documentation when importing modules  
🐛 Bug
I tried to import the following modules.
from pytorch_lightning.accelerators.ddp_accelerator import DDPAccelerator
from pytorch_lightning.cluster_environments import TorchElasticEnvironment

Gives the error : ModuleNotFoundError: No module named 'pytorch_lightning.accelerators.ddp_accelerator'
works well with version 1.1.8
current version = 1.2.0