Reformat source code with black.

This is the result of:

    $ black --line-length 119 examples templates transformers utils hubconf.py setup.py

There's a lot of fairly long lines in the project. As a consequence, I'm
picking the longest widely accepted line length, 119 characters.

This is also Thomas' preference, because it allows for explicit variable
names, to make the code easier to understand.

examples/pplm/pplm_classification_head.py

@@ -1,5 +1,6 @@
 import torch
 
+
 class ClassificationHead(torch.nn.Module):
     """Classification Head for  transformer encoders"""