Unable to use Trainer.predict: 'Trainer' object has no attribute 'predict_dataloaders'
🐛 Bug
Unable to use the new Trainer.predict method with datamodule input. The following error is thrown: AttributeError: 'Trainer' object has no attribute 'predict_dataloaders'
Best I can tell, the error originates from this line: 
  
    
      pytorch-lightning/pytorch_lightning/trainer/predict_loop.py
    
    
         Line 33
      in
      6cc1a06
    
  
  
    

        
          
           dataloaders = self.trainer.predict_dataloaders 
        
    
  


Additionally, the documentation is vague about which dataloader is used from the datamodule.
To Reproduce
https://colab.research.google.com/drive/1ZD5xwVifXnxkbAypyeP-nnAXa1IYCBNx?usp=sharing
Expected behavior
Don't throw an error?
Environment
* CUDA:
	- GPU:
		- Tesla T4
	- available:         True
	- version:           10.1
* Packages:
	- numpy:             1.19.5
	- pyTorch_debug:     False
	- pyTorch_version:   1.7.1+cu101
	- pytorch-lightning: 1.2.2
	- tqdm:              4.41.1
* System:
	- OS:                Linux
	- architecture:
		- 64bit
		- 
	- processor:         x86_64
	- python:            3.7.10
	- version:           #1 SMP Thu Jul 23 08:00:38 PDT 2020


PyTorch Version (e.g., 1.0):
OS (e.g., Linux):
How you installed PyTorch (conda, pip, source):
Build command you used (if compiling from source):
Python version:
CUDA/cuDNN version:
GPU models and configuration:
Any other relevant information:

Additional context